trial

typical early pregnancy; however, many normal pregnancies In an eleven year institutional review study, Doubilet et al.
do not have this rate of doubling. Only half of all normal documented nine viable pregnancies with initial hCG levels
singleton pregnancies will have the hCG level double within that exceeded a discriminatory zone of 2000-3000 mIU/L and
48 hours.(18) When considering a specific threshold for the initial ultrasound showed no gestational sac.(19) Doubilet
normal hCG level increases, Barnhart et al. note that 99 % of et al. suggest using serial ultrasounds and hCG levels to
guide management in a hemodynamically stable pregnant
MOVIE 5.1 Pregnancy Failure patient with a pregnancy of unknown location rather than
using a single level.(19) Another criticism of using a single
Pregnancy Failure discriminatory hCG level to differentiate normal from ectopic
viable early pregnancies will have the hCG level increase at pregnancy is the possibility of missing the diagnosis of a
least 24 % when checked at 24 hours, 53 % when checked at multiple gestation pregnancy and misdiagnosing pregnancy
48 hours, and double at one week.(18) failure or ectopic pregnancy. Multiple gestation pregnancies
Several studies bring the validity of a single discriminatory typically have higher hCG levels than singleton gestation
hCG level between 1000-2000 mIU/ml into question.(19-21) pregnancies at the same gestational age.(22)

Physicians are responding variably to these new
recommendations. Levine, a radiologist, points out that many
radiologists consider these new thresholds overly
conservative which lead to inevitable delays in treatment and
unnecessary repeat scans.(23) Creinin, an obstetrician,
points out that the false positive cases using traditional
thresholds are very uncommon (i.e. nine cases in an eleven
year review of a busy institution).(24) ACOG points out that
the recommendations do not include shared decision making
between clinician and patient.(10) For example, is this
patient reliable to comply with serial hCG levels and
ultrasound? Does the patient desire to continue with the
pregnancy? Does the patient accept the risks of delaying an

50

intervention in order to determine with 100 % accuracy if the A gestational sac (GS) with a 16 mm mean sac diameter

pregnancy is viable? (MSD) using TV ultrasound without an obvious embryo was

Sonographic Findings in Early Pregnancy Failure felt to be diagnostic of pregnancy failure; however this
threshold only had a sensitivity of 50 %.(25) Abdallah et al.

As addressed above, concern documented cases of viable
for premature termination of
viable pregnancies has GALLERY 5.2 Proposed Criteria for Pregnancy Failure pregnancies with MSD > 16 mm
influenced a proposed change using TV ultrasound
in cut-off levels for viable and
nonviable first trimester Proposed Criteria For Possible Pregnancy demonstrating no visible
pregnancies. In 2013, the Failure embryo which progressed to
Society for Radiologist in viable pregnancies.(25) A
Ultrasound Multispecialty Panel
on Early First Trimester CRL < 7 mm without cardiac activity recent study found 19%
Diagnosis of Miscarriage and
Exclusion of a Viable MSD 16-24 mm without an embryo interobserver variability in
Intrauterine Pregnancy
published consensus Absence of embryo with cardiac activity 7-13 days after ultrasound showing gestational sac measuring MSD.(26) By
recommendations (Gallery 5.2). without yolk sac increasing the cutoff for the GS
(13) Using these more
generous thresholds, clinicians Absence of embryo with cardiac activity 7-10 days after ultrasound showing gestational sac mean sac diameter to 25 mm,
lower the risk of terminating a and yolk sac the sensitivity and specificity
approaches 100 % for
Empty amnion (Amnion and yolk sac without embryo) confirming pregnancy failure.

No embryo > 6 weeks after last menstrual period

Yolk Sac > 7 mm (13)

Discordance in Gestational Sac and Embryo Size: CRL and MSD are < 5 mm different Crown-Rump Length (CRL)

Proposed criteria for possible pregnancy failure. (13) Previously a fetal pole with a

viable pregnancy to nearly zero CRL of 5 mm and no fetal

but could potentially delay cardiac activity was felt to be

diagnosis of an ectopic diagnostic of pregnancy failure.

pregnancy and may result in unnecessary additional testing Meta-analysis of published studies demonstrates this cut-off

for pregnancy failure. has a sensitivity of 50% and specificity of 100% with 95%

Gestational Sac and Mean Sac Diameter confidence interval 90-100.(27) Similar to variability in MSD
measurements, Pexsters et al. found 15% interobserver

51

variability in measuring CRL.(26) When using a cutoff of 5 weeks’ gestation. Miscarriage rates range from 8-22% of
mm CRL without cardiac activity, the practitioner could patients who know they are pregnant.(8,10) Understanding
diagnosis pregnancy failure and recommend treatment that the risks of miscarriage is important when counseling patients
could result in termination of a viable pregnancy. This error in who present with vaginal bleeding in first trimester
diagnosis can be nearly erased by increasing the CRL cutoff pregnancies.
to 7 mm at which point the
Threatened Abortion
specificity approaches 100 %.(13) MOVIE 5.2 Miscarriage
Threatened abortion is any
The previous criteria for pregnancy bleeding that occurs in a
failure, CRL of 5 mm and MSD of confirmed pregnancy.
16 mm without visible embryo, Approximately 20% of
have not been discarded. women experience some
However, they are now assigned bleeding during pregnancy.
as measurements suggestive of (2) In women who
pregnancy loss rather than experience any vaginal
diagnostic of pregnancy failure. bleeding in the first trimester,
Shared decision making, about 10% will miscarry;
appropriate anticipatory guidance however, the risk of
and education to patients are miscarriage varies
critical when using these more depending on amount of
conservative guidelines. bleeding present.(2) For
those with only light bleeding
Miscarriage or spotting lasting 1-2 days,
the risk of miscarriage during
Miscarriage (Movie 5.2) the first trimester is similar to those without bleeding.(1) If
heavier bleeding is present, particularly with painful cramping,
Pregnancy complications are very common in the Emergency up to 24% of women will miscarry.(1,28)
Department. Vaginal bleeding in first trimester pregnancies
comprise 1.6% of all ED visits in the US.(7) A spontaneous 52
abortion or miscarriage is a loss of pregnancy prior to 20

Another cause of vaginal bleeding that should be evaluated is vessels associated with retained products of conception
subchorionic hemorrhage. Subchorionic hemorrhage is (RPOC). Sonographic findings of RPOC typically include the
bleeding behind the gestational sac thought to be from partial presence of endometrial vascularity and endometrial
detachment of the chorion.(29) On ultrasound this will appear thickness of 15 mm or greater.(4,33,34) The absence of
as an anechoic or hypoechoic region adjacent to the GS Doppler flow on a thickened endometrium does not rule out
usually crescentic in shape as it tracks along the perimeter of RPOC as they may be avascular. Clinical suspicion, hCG
the GS. This can be found in approximately 9% of first level, and physical exam findings must be integrated with the
trimester pregnancies with vaginal bleeding.(30) clinician’s sonographic findings when evaluating the patient
Subchorionic hemorrhage is associated with an increased risk with possible RPOC.
of first trimester pregnancy loss, estimated at 9% overall risk
with an increased risk up to 19% if the hematoma involves a Complete Abortion
larger circumference of chorion elevation.(29,31)
Complete abortion has sonographic, hormonal, and clinical
Incomplete Abortion findings. On ultrasound, complete abortion will appear as
homogenous intrauterine dimension of less than 15 mm in the
The hallmark of incomplete abortion is that some but not all anteroposterior plane on TV ultrasound with no evidence of
products of conception have passed. Diagnosing an RPOC.(3,5,6,35) Vaginal bleeding stops and the hCG levels
incomplete abortion can be straightforward if a prior drop. Following spontaneous abortions, hCG levels decline
ultrasound demonstrated a viable intrauterine pregnancy and as follows: day 2 levels decline from 21-35% (higher decline
follow up ultrasound reveals debris in the uterus or hCG with higher starting hCG level); day 7 levels decline 60-84%.
levels are falling. On ultrasound, incomplete abortions will (36) In medical abortions, hCG levels also decline rapidly
have varying degrees of endometrial thickness as well as over the first week (mean decline from baseline day one=
potential definitive visualization of placental or fetal tissue.(3) 57%, day 3= 74%, day 5= 86%, day 6 =93%).(37,38)
Clinically, the patient may or may not be bleeding. The mean Following serial hCG levels compared with serial ultrasounds
time to complete a miscarriage with expectant management is to diagnose successful medical abortions revealed no
9 days.(32) difference in detection of RPOC and need for surgical
intervention.(38)
When there is clinical concern for an incomplete miscarriage
and the ultrasound only demonstrates a thickened 53
endometrium, color Doppler can be used to identify feeding

Molar Pregnancy (Gestational Trophoblastic Disease) On ultrasound, the complete molar pregnancy has a complex,
(Movie 5.3) intrauterine, echogenic mass that contains many small cystic
structures.(42) This cystic appearance resembles a cluster of
In the United States, the incidence of molar pregnancy is 1 in grapes. The typical “snowstorm” appearance of complete
molar pregnancies is usually apparent in the second trimester
1000.(39) The frequency of MOVIE 5.3 Molar Pregnancy
these pregnancies is higher in with greater variability in
appearance in the first
Southeast Asia.(39,40) A molar trimester.(42) The partial molar
pregnancy is much more
pregnancy is nonviable and difficult to diagnose on
ultrasound, and is often
represents a significant risk to diagnosed by tissue biopsy
after pregnancy failure.
the mother. Pregnancies can Sonographic findings often
include an abnormally enlarged
be complete or partial placenta, enlarged uterus,
occasionally a gestational sac
hydatidiform moles, with and small for gestational age
fetus and hydropic villi.(43)
increased rates of malignancy in Given the variability in
appearance both complete and
complete moles.(41) A clinician partial moles can be confused
for RPOC and pregnancy
should have suspicion for a failure.

molar pregnancy when the hCG Theca lutein cysts are frequently seen in patients with molar
pregnancies.(41,42)  They are thought to originate due to the
levels are significantly higher excessive amounts of circulating hormone and can also been
seen in other medical conditions associated with elevated
than expected for the estimated

gestational age. However, in a

partial hydatidiform molar

pregnancy, the hCG levels can Molar Pregnancy
be within the normal expected

range.(41) Patients with molar

pregnancy often present with exaggerated signs of

pregnancy, vaginal bleeding, and a nonviable pregnancy. In

the second trimester, patients may present with signs of pre-

eclampsia, anemia, and hyperthyroidism.(41)

54

circulating hormone levels.  These cysts are usually seen ultrasound criteria for diagnosing an "empty uterus". Am J
bilaterally and are thin walled with anechoic contents. Obstet Gynecol. 2004;191(4):1133-1137.

References: 7." Wittels KA, Pelletier AJ, Brown DF, Camargo CA, Jr.
United States emergency department visits for vaginal
1." Hasan R, Baird DD, Herring AH, Olshan AF, Jonsson bleeding during early pregnancy, 1993-2003. Am J Obstet
Funk ML, Hartmann KE. Association between first-trimester Gynecol. 2008;198(5):523 e521-526.
vaginal bleeding and miscarriage. Obstet Gynecol.
2009;114(4):860-867. 8." Wilcox AJ, Weinberg CR, O'Connor JF, et al. Incidence
of early loss of pregnancy. N Engl J Med. 1988;319(4):
2." Poulose T, Richardson R, Ewings P, Fox R. Probability of 189-194.
early pregnancy loss in women with vaginal bleeding and a
singleton live fetus at ultrasound scan. J Obstet Gynaecol. 9." Stephenson MD, Awartani KA, Robinson WP.
2006;26(8):782-784. Cytogenetic analysis of miscarriages from couples with
recurrent miscarriage: a case-control study. Hum Reprod.
3." Jauniaux E, Johns J, Burton GJ. The role of ultrasound 2002;17(2):446-451.
imaging in diagnosing and investigating early pregnancy
failure. Ultrasound Obstet Gynecol. 2005;25(6):613-624. 10." Committee on Practice B-G. The American College of
Obstetricians and Gynecologists Practice Bulletin no. 150.
4." Blohm F, Friden B, Platz-Christensen JJ, Milsom I, Early pregnancy loss. Obstet Gynecol. 2015;125(5):
Nielsen S. Expectant management of first-trimester 1258-1267.
miscarriage in clinical practice. Acta Obstet Gynecol Scand.
2003;82(7):654-658. 11." Nybo Andersen AM, Wohlfahrt J, Christens P, Olsen J,
Melbye M. Maternal age and fetal loss: population based
5." Nielsen S, Hahlin M. Expectant management of first- register linkage study. BMJ. 2000;320(7251):1708-1712.
trimester spontaneous abortion. Lancet. 1995;345(8942):
84-86. 12." Maconochie N, Doyle P, Prior S, Simmons R. Risk
factors for first trimester miscarriage--results from a UK-
6." Leung SW, Pang MW, Chung TK. Retained products of population-based case-control study. BJOG. 2007;114(2):
gestation in miscarriage: an evaluation of transvaginal 170-186.

55

13." Doubilet PM, Benson CB, Bourne T, et al. Diagnostic 20." Mehta TS, Levine D, Beckwith B. Treatment of ectopic
criteria for nonviable pregnancy early in the first trimester. N pregnancy: is a human chorionic gonadotropin level of 2,000
Engl J Med. 2013;369(15):1443-1451. mIU/mL a reasonable threshold? Radiology. 1997;205(2):
569-573.
14." Bateman BG, Nunley WC, Jr., Kolp LA, Kitchin JD, 3rd,
Felder R. Vaginal sonography findings and hCG dynamics of 21." Connolly A, Ryan DH, Stuebe AM, Wolfe HM.
early intrauterine and tubal pregnancies. Obstet Gynecol. Reevaluation of discriminatory and threshold levels for serum
1990;75(3 Pt 1):421-427. beta-hCG in early pregnancy. Obstet Gynecol. 2013;121(1):
65-70.
15." Brennan DF. Ectopic pregnancy--Part II: Diagnostic
procedures and imaging. Acad Emerg Med. 1995;2(12): 22." Celen S, Engin-Ustun Y, Turkcapar F, et al. First
1090-1097. trimester biochemical markers in twin pregnancies. Ginekol
Pol. 2015;86(5):362-365.
16." Committee ACP, Clinical Policies Subcommittee on Early
Pregnancy. American College of Emergency P. Clinical policy: 23." Levine D. Waiting, not rushing, to diagnose a failed
critical issues in the initial evaluation and management of pregnancy. Ultrasound Q. 2014;30(1):11-12.
patients presenting to the emergency department in early
pregnancy. Ann Emerg Med. 2003;41(1):123-133. 24." Creinin MD. Further evidence against the reliability of the
human chorionic gonadotropin discriminatory level. J
17." Barnhart KT, Simhan H, Kamelle SA. Diagnostic Ultrasound Med. 2012;31(5):816-817; author reply 817-818.
accuracy of ultrasound above and below the beta-hCG
discriminatory zone. Obstet Gynecol. 1999;94(4):583-587. 25." Abdallah Y, Daemen A, Kirk E, et al. Limitations of
current definitions of miscarriage using mean gestational sac
18." Barnhart KT, Sammel MD, Rinaudo PF, Zhou L, Hummel diameter and crown-rump length measurements: a
AC, Guo W. Symptomatic patients with an early viable multicenter observational study. Ultrasound Obstet Gynecol.
intrauterine pregnancy: HCG curves redefined. Obstet 2011;38(5):497-502.
Gynecol. 2004;104(1):50-55.
26." Pexsters A, Luts J, Van Schoubroeck D, et al. Clinical
19." Doubilet PM, Benson CB. Further evidence against the implications of intra- and interobserver reproducibility of
reliability of the human chorionic gonadotropin discriminatory transvaginal sonographic measurement of gestational sac
level. J Ultrasound Med. 2011;30(12):1637-1642.
56

and crown-rump length at 6-9 weeks' gestation. Ultrasound and value of follow-up visits. Ultrasound Obstet Gynecol.
Obstet Gynecol. 2011;38(5):510-515. 2002;19(6):580-582.

27." Jeve Y, Rana R, Bhide A, Thangaratinam S. Accuracy of 33." Atri M, Rao A, Boylan C, Rasty G, Gerber D. Best
first-trimester ultrasound in the diagnosis of early embryonic predictors of grayscale ultrasound combined with color
demise: a systematic review. Ultrasound Obstet Gynecol. Doppler in the diagnosis of retained products of conception. J
2011;38(5):489-496. Clin Ultrasound. 2011;39(3):122-127.

28." Gracia CR, Sammel MD, Chittams J, Hummel AC, 34." Kamaya A, Petrovitch I, Chen B, Frederick CE, Jeffrey
Shaunik A, Barnhart KT. Risk factors for spontaneous abortion RB. Retained products of conception: spectrum of color
in early symptomatic first-trimester pregnancies. Obstet Doppler findings. J Ultrasound Med. 2009;28(8):1031-1041.
Gynecol. 2005;106(5 Pt 1):993-999.
35." Nielsen S, Hahlin M, Platz-Christensen J. Randomised
29." Tuuli MG, Norman SM, Odibo AO, Macones GA, Cahill trial comparing expectant with medical management for first
AG. Perinatal outcomes in women with subchorionic trimester miscarriages. Br J Obstet Gynaecol. 1999;106(8):
hematoma: a systematic review and meta-analysis. Obstet 804-807.
Gynecol. 2011;117(5):1205-1212.
36." Barnhart K, Sammel MD, Chung K, Zhou L, Hummel AC,
30." Ben-Haroush A, Yogev Y, Mashiach R, Meizner I. Guo W. Decline of serum human chorionic gonadotropin and
Pregnancy outcome of threatened abortion with subchorionic spontaneous complete abortion: defining the normal curve.
hematoma: possible benefit of bed-rest? Isr Med Assoc J. Obstet Gynecol. 2004;104(5 Pt 1):975-981.
2003;5(6):422-424.
37." Pocius KD, Maurer R, Fortin J, Goldberg AB, Bartz D.
31." Bennett GL, Bromley B, Lieberman E, Benacerraf BR. Early serum human chorionic gonadotropin (hCG) trends after
Subchorionic hemorrhage in first-trimester pregnancies: medication abortion. Contraception. 2015;91(6):503-506.
prediction of pregnancy outcome with sonography. Radiology.
1996;200(3):803-806. 38." Dayananda I, Maurer R, Fortin J, Goldberg AB. Medical
abortion follow-up with serum human chorionic gonadotropin
32." Luise C, Jermy K, Collons WP, Bourne TH. Expectant compared with ultrasonography: a randomized controlled trial.
management of incomplete, spontaneous first-trimester Obstet Gynecol. 2013;121(3):607-613.
miscarriage: outcome according to initial ultrasound criteria
57

39." Atrash HK, Hogue CJ, Grimes DA. Epidemiology of
hydatidiform mole during early gestation. Am J Obstet
Gynecol. 1986;154(4):906-909.

40." Nirmala CK, Nor Azlin MI, Harry SR, et al. Outcome of
molar pregnancies in Malaysia: a tertiary centre experience. J
Obstet Gynaecol. 2013;33(2):191-193.

41." Sun SY, Melamed A, Joseph NT, et al. Clinical
Presentation of Complete Hydatidiform Mole and Partial
Hydatidiform Mole at a Regional Trophoblastic Disease
Center in the United States Over the Past 2 Decades. Int J
Gynecol Cancer. 2016;26(2):367-370.

42." Benson CB, Genest DR, Bernstein MR, Soto-Wright V,
Goldstein DP, Berkowitz RS. Sonographic appearance of first
trimester complete hydatidiform moles. Ultrasound Obstet
Gynecol. 2000;16(2):188-191.

43." Muminhodzic L, Bogdanovic G. Ultrasonographic signs
of partial hydatidiform mole. Med Arch. 2013;67(3):205-208.

58

CHAPTER 6

Ectopic Pregnancy

Thompson Kehrl, MD

SECTION 1
Ectopic Pregnancy

KEY POINTS Ectopic pregnancy is an important cause of maternal
morbidity and mortality in the United States. It occurs when a
1. The majority of ectopic pregnancies are fertilized ovum implants on any tissue other than the
tubal in location. endometrial lining of the uterus. Ectopic pregnancies account
for approximately 1 to 2% of all pregnancies, but cause
2. Serum hCG levels are variable and not approximately 3% of pregnancy-related deaths.(1) Despite
predictive of pregnancy location. an increase in the incidence of ectopic pregnancy in the
United States, there has been a significant decline in mortality
3. Ultrasound cannot be used to definitively since the 1980’s.(2) The cause for increased incidence has
rule out the presence of ectopic pregnancy been attributed to increases in risk factors, including prior
in all cases. sexually transmitted diseases, use of assisted reproductive
techniques, prior tubal surgery, tobacco abuse, intrauterine
device use, and previous ectopic pregnancy.(3,4) However,
half of patients diagnosed with ectopic pregnancy have no
risk factors at all, so it is important that clinicians always
consider the possibility of ectopic pregnancy when evaluating
the symptomatic first trimester patient.(3,4)

60

Patients with ectopic pregnancy will usually present with The liberal use of ultrasound and hormonal testing in this
patient population has played a significant role in the recent
acute lower abdominal pain or vaginal bleeding (Movie 6.1). decline in maternal mortality.(6) Centers with ectopic
pregnancy monitoring programs have managed more patients
While the clinical triad of vaginal bleeding, lower abdominal successfully non-surgically and decreased their negative

pain, and adnexal mass is considered to be specific for the laparoscopy rates.(7) Ultrasound
plays an integral role in the
diagnosis of ectopic pregnancy, the presence of any of these evaluation of the symptomatic first
trimester pregnancy. Serum hCG
findings should prompt levels are generally obtained in
pregnant patients with possible
further investigation to MOVIE 6.1 Ectopic Pregnancy ectopic pregnancy and utilized in
exclude ectopic pregnancy. conjunction with ultrasound
findings. A single hCG level may
In a 1980 study of 283 be viewed as a guide to gestational
age but gives no information on
patients presenting with pregnancy location. The
emergency clinician must be
symptoms concerning for careful when utilizing serum hCG
level since levels in women with
ectopic pregnancy, the ectopic pregnancy are extremely
variable and not predictive of
clinical triad had a positive rupture.(6, 8) The presence of a
low quantitative hCG level should
predictive value of only 14%. not dissuade the emergency clinician from performing a pelvic
ultrasound in a symptomatic patient.
(5) A 2006 study notes the
There are multiple possible anatomic locations for ectopic
following odds ratios in pregnancy, with tubal being most common (90-95 %).(9)

comparing patients with 61

ectopic pregnancy with other

symptomatic pregnancy

patients: prior ectopic

pregnancy (2.98), history of

pelvic inflammatory disease Ectopic pregnancy introduction.
(1.5), pain at presentation

(1.4), vaginal bleeding at

presentation (1.42) and human chorionic gonadotropin (hCG)

level between 501-2000 mIU/ml (1.73).(4) In patients with

shock and symptoms concerning for ectopic pregnancy,

standard resuscitative measures should be undertaken with

early obstetric consultation for operative intervention.

Non-tubal locations include interstitial, ovarian, cervical, findings suspicious for an ectopic pregnancy, or a normal
cesarean section scar and abdominal (Gallery 6.1). pelvic ultrasound (pregnancy of unknown location).
Ultrasound frequently is helpful in confirming the location of
Free Fluid (Movie 4.5)
GALLERY 6.1 Ectopic Pregnancy Implantation Sites Clinical Pearls:

Illustration depicting ectopic pregnancy implantation sites. 1." Identifying peritoneal free fluid is a key part of point-of-
the pregnancy and “ruling in” an ectopic pregnancy, but it is care first trimester ultrasound.
essential to understand that ultrasound alone cannot be used
to “rule out” the presence of an ectopic pregnancy. 2." Free fluid can either appear anechoic or echogenic.
Sonographic findings in patients with ectopic pregnancy may
include definitive visualization of the ectopic pregnancy, 3." Echogenic free fluid should be considered to be
hemoperitoneum until proven otherwise in a patient with
suspected ectopic pregnancy.

4." The presence of fluid in Morison’s pouch is highly
predictive of the need for operative intervention in patients
with suspected ectopic pregnancy.

In addition to identifying the presence or absence of an
intrauterine pregnancy, one of the main goals of point-of-care
first trimester ultrasound is evaluating the female pelvis for the
presence of free fluid. Identifying and quantifying free fluid
should be part of every focused first trimester ultrasound
examination. The sonologist should start by examining the
pouch of Douglas (or posterior cul-de-sac) for the presence of
free fluid since this is the most dependent portion of the pelvis
in the supine patient. Physiological free fluid is commonly
seen in both the pregnant and non-pregnant female pelvis
and is typically seen low in the pelvis. As the amount of fluid

62

in the pelvis increases, it extends along the posterior uterine pelvic views and should be included in any exam when more
wall towards the uterine fundus. Free fluid is considered than a small amount of free fluid is visualized in the pelvis.
small if it extends one-third up the posterior uterine wall, Identification of fluid in Morison’s pouch is predictive of the
moderate if it extends two-thirds up the posterior uterine wall need for operative intervention in patients with suspected
and large if it extends beyond two-thirds of the posterior wall, ectopic pregnancy and should lead to prompt obstetrical
spills into the anterior cul-de-sac or extends up into Morison’s consultation.(13)
pouch.(10) It is important to evaluate the anterior cul-de-sac
in patients with a normal posterior cul-de-sac as some Endometrial Findings (Movie 6.2)
patients may have free fluid isolated to the anterior cul-de-
sac, particularly in patients with a retroverted uterus.(11) Clinical Pearls:

Sonographically, fluid can either appear anechoic (simple) or 1." Endometrial thickness cannot be used to rule in or rule
echogenic (complex). Distinguishing between simple and out the presence of an ectopic pregnancy.
complex free fluid is imperative. Echogenic free fluid in the
setting of a pregnant patient with abdominal pain accurately 2." Pseudogestational sacs are seen in about 10% of
correlates with hemoperitoneum and should be considered to ectopic pregnancies.
be hemoperitoneum until proven otherwise.(11) Other causes
of complex free fluid include a ruptured hemorrhagic corpus 3." Trilaminar appearance of the endometrium is specific but
luteum cyst, pelvic inflammatory disease, and ovarian torsion. not sensitive for the diagnosis of ectopic pregnancy.
The rate of ruptured ectopic pregnancy in patients with
moderate to large free fluid is significantly higher than in In patients with a clinically suspected ectopic pregnancy and
patients with only trace to mild free fluid.(12) When no definitive sonographic evidence of an intrauterine or
hemoperitoneum has had time to clot, a pelvic hematoma can extrauterine pregnancy, evaluation of the endometrial pattern
form which will appear as an echogenic fluid collection. This or thickness may provide useful information. Sonographic
isoechoic or hyperechoic fluid may be misleading to the findings of the endometrium in patients with ectopic
novice sonologist and care must be taken to avoid the pitfall pregnancy include the presence of a pseudogestational sac, a
of only evaluating for anechoic free fluid. normal endometrium, a thickened endometrium, a thinned
endometrium, or a trilaminar endometrium. Additionally, the
Imaging the right upper quadrant to evaluate for peritoneal endometrium may have either a homogenous or
free fluid is an important adjunctive view to the standard heterogeneous appearance.

63

Numerous studies have evaluated endometrial thickness as a located eccentrically within the endometrial canal. In the
predictor of ectopic pregnancy.(14-17) These studies have setting of an ectopic pregnancy, a false, or pseudogestational,
shown that the width of the endometrial stripe is thinner in sac can form. A pseudogestational sac is thought to be the
patients with ectopic pregnancies, but no specific cut-off value result of fluid in the endometrial canal caused by endometrial
could be determined.(14-17) Therefore, endometrial breakdown. The sonographic finding was first described in
thickness should not be used to rule-in or rule-out the 1979 with a reported incidence of approximately 20 %.(18)
presence of an ectopic pregnancy in patients with pregnancy More recent studies have found a lower frequency of
of unknown location. approximately 10 %.(19-21)
A gestational sac is one of the earliest sonographic findings in
A pseudogestational sac can potentially be confused with a
MOVIE 6.2 Endometrial Findings normal gestation sac. The shape and location of the sac may
be helpful in distinguishing between the two types of sacs.
Endometrial findings in ectopic pregnancy. Pseudogestational sacs are typically located centrally within
a normally developing intrauterine pregnancy. It is usually the endometrial canal, as opposed to true gestational sacs
which tend to implant eccentrically within the endometrial
cavity. (slideshow) The shape of the sac is important, as a
pseudogestational sac is often oval, has pointy edges, and
conforms to the shape of the uterine cavity while a normal
gestational sac is typically round. Pseudogestational sacs
can be of a variety of sizes and therefore size cannot be used
to distinguish a gestational sac from a pseudogestational sac.
In a recent evaluation of 229 patients with ectopic pregnancy,
only 2 patients (0.9%) had smooth walled anechoic fluid
within the uterus which could be confused for a normally
developing gestational sac.(22) From a statistical standpoint,
the presence of an intrauterine anechoic sac is much more
likely to be a developing normal IUP and not a
pseudogestational sac.(22)

64

The trilaminar endometrium is formed during the late 4." The tubal ring sign or “ring of fire” is very sensitive but
proliferative phase of the normal menstrual cycle. It consists poorly specific for the diagnosis of a tubal ectopic pregnancy.
of an echogenic basal layer and a hypoechoic inner layer that
is surrounded by a thin echogenic layer that represents the The majority of ectopic pregnancies are tubal in location
interface with the endometrial lumen. (slideshow) The (>90%) with implantation occurring in the isthmic, ampullary,
trilaminar endometrial pattern can also develop in patients or fimbrial portions of the fallopian tube.(25) The sonographic
with ectopic pregnancy. This pattern is highly specific (>
90 %) but poorly sensitive (approximately 20%) for the MOVIE 6.3 Tubal Ectopic Pregnancy
diagnosis of ectopic pregnancy.(16,23,24) In the prediction of
ruptured ectopic pregnancy, a trilaminar endometrial pattern
had a sensitivity of 60%, a specificity of 95.7%, a positive
predictive value of 85.7%, and a negative predictive value of
84.6%.(24) Therefore, in patients without sonographic
evidence of an intrauterine pregnancy, the diagnosis of
ectopic pregnancy should be strongly considered when this
trilaminar endometrial pattern is present

Tubal Ectopic (Movie 6.3) Tubal ectopic pregnancy.
Clinical Pearls:
1." Definitive evidence of ectopic pregnancy includes appearances of the tubal ectopic pregnancy will depend on
visualization of an adnexal mass containing a yolk sac or the gestational age of the pregnancy, the location of
viable embryo. implantation in the tube, and the viability of the pregnancy.

2." Suspicious findings of ectopic pregnancy include Definitive sonographic findings of tubal ectopic pregnancy
adnexal masses and tubal rings. include a tubal mass with a visible yolk sac or embryo, with or

3." Transducer mobilization may help distinguish a tubal 65
ectopic pregnancy from a corpus luteum cyst.

without cardiac activity. These findings carry positive poorly specific for the diagnosis of a tubal ectopic pregnancy.
predictive values (PPV) for ectopic pregnancy of 100% but This sign can be seen in both corpus luteum cysts and tubal
are only seen in approximately 13-22% of ectopic ectopic pregnancy and should not be used to distinguish
pregnancies.(12,26,27) between the two entities.(9) Color Doppler may also allow for
detection of a tubal ectopic pregnancy surrounded by loops of
Sonographic findings that are suspicious but not definitive for bowel. However, the presence of significant bowel peristalsis
tubal ectopic pregnancy include tubal rings and adnexal will result in artifact that may obscure the “ring of fire.”
masses. A tubal ring without yolk sac separate from the
ipsilateral ovary is seen in approximately 20-25% of cases Interstitial Ectopic (6.4)
and carries a PPV of 90-95%.(12,26,27) Sonographically the Clinical Pearls:
tubal ring appears as a hypoechoic circular structure with
hyperechoic outer ring. The most common finding of an 1." An interstitial ectopic is a dangerous subtype of ectopic
ectopic pregnancy, seen in approximately 54-58% of cases, is pregnancy in which the ovum implants in the portion of the
a nonspecific complex or solid adnexal mass and has a PPV fallopian tube that traverses the uterine wall.
of 90-95%.(12,26,27)
2." Ultrasound findings include an eccentrically located
The corpus luteum is an integral part of the development of gestational sac with less than 5 mm of myometrium
normal pregnancy and it can have multiple different surrounding the gestational sac.
sonographic appearances. A corpus luteum cyst can be very
difficult to distinguish from the non-specific adnexal mass of a 3." A cornual pregnancy occurs in a horn of a bicornuate
tubal ectopic pregnancy.(28) Transducer pressure can be uterus and is associated with a better prognosis compared to
employed to help distinguish between a corpus luteum cyst that of an interstitial ectopic.
and a tubal mass with attempts made to mobilize the
suspected tubal mass. If the mass moves with the ovary, it is An interstitial ectopic pregnancy occurs when a fertilized
likely a corpus luteum cyst. An ectopic pregnancy will move ovum implants in the myometrial portion of the fallopian tube
separately from the ovary.(29) where it traverses the wall of the uterus to enter the
endometrium and is estimated to comprise 2-4% of ectopic
Traditionally, color Doppler has been used to visualize the pregnancies.(30) Patients with interstitial pregnancies that
vascular flow around a tubal ring or adnexal mass and is advance past 12 weeks of gestational age are at particularly
described as “ring of fire.” “Ring of fire” is very sensitive but
66

high risk for rupture. The insertion site for interstitial while interstitial ectopic pregnancies do not result in viable
pregnancies tends to be located closely to the uterine artery pregnancies.(32)
and rupture can cause brisk hemorrhage, leading to
increased morbidity and mortality compared to ruptured tubal Sonographic recognition and diagnosis of interstitial
pregnancies.(31) While interstitial ectopic pregnancy and pregnancy is challenging as the gestational sac is located
outside of the endometrium but still within the uterus;
MOVIE 6.4 Interstitial Ectopic Pregnancy therefore careful analysis of the surrounding anatomy is key.
(33) Criteria for diagnosis of an interstitial pregnancy include
Interstitial ectopic pregnancy. an empty uterus, an eccentrically located gestational sac, and
cornual pregnancy are often used interchangeably, they are a thin myometrial mantle.(34) The myometrial mantle is
two distinct entities and should not be confused. Cornual measured at the thinnest portion of myometrium from the free
pregnancies are pregnancies that occur in a horn of a uterine wall to the endometrium. A measurement of 5 mm or
bicornuate uterus. They are associated with higher less should be considered highly suspicious for the presence
complication rates but can still result in viable pregnancies, of an interstitial ectopic pregnancy. Some have suggested
using an 8 mm cutoff; while this would increase the sensitivity
it would also result in a higher false-positive rate.(30) The
currently used cutoff criteria is based on data from small
studies and case series and there is no prospective study
available that offers a conclusive measurement.(9) Uterine
contractions resulting in an eccentrically located but normally
implanted gestational sac, an early intrauterine pregnancy in
a bicornuate uterus, and a uterine fibroid in a pregnant patient
without a visualized intrauterine pregnancy can all be
mistaken for an interstitial ectopic pregnancy. In cases where
the 2D ultrasound is inconclusive, 3D ultrasound or MRI may
play a role.(31)

67

The interstitial portion of the fallopian tubes is visualized A cervical ectopic pregnancy occurs when there is
sonographically as an echogenic line that connects implantation of a fertilized ovum in the endocervical canal and
endometrium to the uterine serosa. An interstitial ectopic may represents less than 1% of ectopic pregnancies.(36) Patients
be visualized in the middle of this echogenic line, termed the usually present with painless vaginal bleeding during the first
interstitial line sign, and is thought to be very specific for the trimester. Cervical ectopic is considered a high-risk subtype
diagnosis of interstitial pregnancy.(35)
MOVIE 6.5 Miscellaneous Ectopic Pregnancies
Miscellaneous Ectopic Pregnancies (Movie 6.5)
Cervical, ovarian, cesarean section scar, and abdominal ec-
Clinical Pearls: topic pregnancies.
of ectopic pregnancy because of the increased vascularity of
1." Non-tubal ectopic pregnancies are rare. the cervix and the amount of bleeding that can occur with
rupture.(37)
2." Knowledge of potential locations and sonographic
appearances of non-tubal ectopic pregnancies is important 68
when performing point-of-care first trimester ultrasound.

3." Because of anatomical considerations, non-tubal ectopic
pregnancies are associated with increased morbidity and
mortality.

Less than 10% of ectopic pregnancies involve implantation of
the fertilized egg in locations other than the fallopian tubes.(6)
These locations include the cervix, cesarean section scar,
ovary, and abdomen. Despite their rarity, knowledge of the
sonographic appearance of these ectopic pregnancies is
important when performing point-of-care first trimester
ultrasound as they can be challenging to diagnose.

Cervical Ectopic

A cervical ectopic pregnancy can easily be confused with the in the anterior myometrium and subsequent implantation at
cervical phase of a spontaneous miscarriage.(38) Findings this site.(40) Findings on pelvic ultrasound include an empty
suggestive of a spontaneous abortion include an irregularly uterine cavity, an empty cervical canal, development of a
shaped gestational sac that is not adherent to the cervix. gestational sac in the anterior portion of the uterine isthmus at
Clinically, an open cervical os strongly suggests spontaneous the presumed site of cesarean scar, and absence of healthy
abortion. If an embryo with cardiac activity is visualized below myometrium between the bladder and the gestational sac.(40)
the internal cervical os, cervical ectopic is the diagnosis. If the The gestation can develop prominent vascularity; thus
gestational sac is in the same position and has the same bleeding can be severe when cesarean scar pregnancies
shape on repeat ultrasound examination, cervical ectopic is rupture.(40) Additionally, there is high risk of significant
likely.(37) Correct diagnosis is imperative, since treating a maternal morbidity and mortality if rupture occurs.(40)
cervical ectopic as a cervical phase of a spontaneous
abortion with dilation and curettage can cause severe life- Ovarian Ectopic
threatening hemorrhage.(33)
Ovarian ectopic pregnancy occurs when a fertilized ovum is
Nabothian cysts can be confused with the sac of a cervical retained in an ovary. Ovarian ectopic pregnancy is estimated
ectopic. Nabothian cysts, however, will not have an to comprise 1-3% of ectopic pregnancies and is associated
echogenic ring present and are frequently far enough away with IUD usage.(25) Sonographically, most ovarian ectopic
from the cervical canal to prevent confusion. pregnancies appear cystic and have an echogenic outer ring.
A yolk sac or embryo is not commonly visualized. Applying
Cesarean Scar Ectopic transducer pressure augmented by manual abdominal
pressure can help distinguish between a tubal and an ovarian
Cesarean scar pregnancy occurs when there is implantation ectopic.(33) However, it can be very difficult to distinguish
of a fertilized ovum in the anterior lower uterine segment at between a corpus luteum and an ovarian ectopic and some
the site of a cesarean scar. Cesarean scar pregnancies patients will need repeat ultrasound examinations to assess
represent 6% of ectopic pregnancies in women with a prior for sonographic changes in the concerning ovarian mass.(41)
cesarean section.(39) The incidence is low, representing less
than 1% of all ectopic pregnancies, but thought to be rising Abdominal Ectopic
because of increasing rates of cesarean deliveries.(39) The
underlying pathophysiology is unknown but the predominant Abdominal ectopic pregnancy occurs when there is
theory is that poor healing of the scar leads to a wedge defect implantation of a fertilized ovum anywhere in peritoneal cavity.
Abdominal ectopics are exceedingly rare, representing < 1%

69

of all ectopic pregnancies.(25) Abdominal ectopic pregnancy Heterotopic pregnancy is by definition the presence of an
can be defined as primary or secondary.(42) Primary intrauterine and simultaneous ectopic pregnancy. Risk of
abdominal ectopic pregnancy is very rare and occurs when a spontaneous heterotopic pregnancy is about 1 in 30,000;
fertilized ovum implants itself initially on an abdominal organ, however, risk in women receiving assisted reproductive
while secondary abdominal ectopic pregnancy occurs when technology (ART) is significantly increased at 1 to 3 in 1000.
the fertilized ovum is implanted in the fallopian tube or uterus (45) Because of its rarity, diagnosis is often delayed and most
and then escapes into the peritoneal cavity through rupture. cases are missed on initial presentation.(46) Both ectopic
(42) Anatomically, they are most commonly found in the and heterotopic pregnancies are considered serious
posterior cul-de-sac or adjacent to the fundus of the uterus. complications of ART. Rupture of the ectopic pregnancy can
(43) Diagnosis tends to be delayed and inaccurate. have deleterious effects on the intrauterine pregnancy;
Abdominal ectopic pregnancies are associated with high however, if expeditiously diagnosed and treated properly, the
maternal mortality, upwards of 18%, because of the intrauterine pregnancy can frequently be brought to term.
aforementioned delay in diagnosis as well as anatomic
considerations leading to a high rate of rupture and Women undergoing ART are potentially at increased risk of
subsequent hemorrhage.(44) ectopic pregnancy given the high likelihood of underlying
tubal dysfunction. When ovarian hyperstimulation and
Heterotopic Pregnancy (Movie 6.6) embryonic transfer techniques are utilized, the risks of both
Clinical Pearls: ectopic pregnancy and heterotopic pregnancy are increased.
1." Heterotopic pregnancy is defined as the presence of (47)
both an IUP and simultaneous ectopic pregnancy.
Routine evaluation of the adnexa during first-trimester point-
2." Heterotopic pregnancies are rare but occur with much of-care ultrasound will help evaluate for the potential of
more frequency in patients undergoing assisted reproduction. heterotopic pregnancy, with particular attention given to
patients undergoing ART. Even in the presence of
3." In symptomatic patients undergoing assisted intrauterine pregnancy, echogenic and/or a moderate amount
reproduction, pelvic ultrasound should thoroughly examine of pelvic free fluid should prompt the sonologist to further
the pelvis. scrutinize the adnexa.(48)

70

Pregnancy of Unknown Location presenting to an urban academic emergency department

Clinical Pearls: noted a PUL rate of 20%.(50) The outcomes of patients with

1." Pregnancy of unknown location (positive hCG level and PUL in this study were poor, with approximately 50%
a normal uterus and adnexa on ultrasound) is a complex pregnancy failure, 15% ectopic pregnancy, and 30% IUP.(50)
clinical scenario. Notably, fewer patients in the PUL follow-up group with

ectopic pregnancy required

2." Every effort should be made MOVIE 6.6 Heterotopic Pregnancy surgical treatment (36% vs
to eliminate false positive results 83%).(50)

(inappropriate diagnosis of non- For patients with PUL,
viability). deciding whether therapy for

3." When in doubt, a repeat hCG ectopic pregnancy should be
level and ultrasound is indicated. initiated is the key question.
If there is a chance of a

When a pregnancy cannot be viable IUP, conservative

definitely called intrauterine, management is paramount

ectopic, or failed, the location of and should include a follow-

the pregnancy is temporarily up hCG level and ultrasound.

unable to be identified, thus termed The consequences of a false

pregnancy of unknown location positive (i.e. an inappropriate

(PUL). Between 5-42% of diagnosis of non-viability) are

symptomatic pregnant women severe, as treating a desired

being evaluated for abnormal first Heterotopic pregnancy. viable IUP as an ectopic
trimester pregnancy are diagnosed pregnancy can have

with PUL.(49) Compared with catastrophic repercussions.

ectopic pregnancies that are identified on initial ultrasound, The consequence of a false negative (i.e. incorrect diagnosis

ectopic pregnancies which are initially diagnosed as PUL of potential viability) is much less dire and usually amounts to

have lower mean gestational age and mean initial hCG level. close follow-up with a minimal delay in treatment for a patient

(26) A 2004 study of symptomatic first trimester patients without an adnexal mass on ultrasound. Clinical decision

71

trees are currently being evaluated to stratify PUL into low of a false positive ectopic pregnancy with the risks of missing
and high risk for ectopic pregnancy and monitor for adverse the window of opportunity for using methotrexate is key.
outcomes.(51-53) Test specificity for ectopic pregnancy
needs to be as close to 100% as possible, and all attempts References:
should be made to eliminate any chance of a false positive
result.(54) 1 Creanga AA, Berg CJ, Syverson C, Seed K, Bruce FC,
Callaghan WM. Pregnancy-related mortality in the United
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regarding PUL and the “discriminatory zone.” The
discriminatory zone is the hCG level above which an 2 Creanga AA, Shapiro-Mendoza CK, Bish CL, Zane S, Berg
intrauterine gestational sac should be seen on US in normal CJ, Callaghan WM. Trends in ectopic pregnancy mortality in
pregnancy. Traditional levels are 6500 mIU/ml IRP for the United States: 1980-2007. Obstet Gynecol. 2011 Apr;
transabdominal imaging and between 1000-2000 mIU/ml IRP 117(4):837-43.
for transvaginal imaging. These single value thresholds are
not acceptable given the need to limit false positive diagnoses 3 Ankum WM, Mol BW, Van der Veen F, Bossuyt PM. Risk
of nonviable pregnancies. There are published cases of term factors for ectopic pregnancy: a meta-analysis. Fertil Steril.
deliveries after an initially empty uterus and hCG levels above 1996 Jun;65(6):1093-9.
3000 mIU/mL IRP. Even in a patient with a PUL and an hCG
level of greater than 2000 mIU/ml, a nonviable IUP is twice as 4 Barnhart KT, Sammel MD, Gracia CR, Chittams J, Hummel
likely as an ectopic pregnancy. For a patient with PUL and an AC, Shaunik A. Risk factors for ectopic pregnancy in women
hCG level between 2000-3000 mIU/ml, the likelihood of viable with symptomatic first-trimester pregnancies. Fertil Steril.
IUP is 2%, ectopic pregnancy is 32% and nonviable IUP is 2006 Jul;86(1):36-43.
66%.(55) In contrast, for a patient with PUL and an hCG level
greater than 3000 mIU/ml, the likelihood of an IUP is 0.5%. 5 Schwartz RO, Di Pietro DL. beta-hCG as a diagnostic aid
(55) Multiple gestations are also associated with higher hCG for suspected ectopic pregnancy. Obstet Gynecol. 1980 Aug;
levels.(55) 56(2):197-203.

The management of patients with PUL should include 6 Barnhart KT. Clinical practice. Ectopic pregnancy. N Engl J
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MP, Johnson SC. The role of sonographic endometrial
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11 Sickler GK, Chen PC, Dubinsky TJ, Maklad N. Free 17 Mol BW, Hajenius PJ, Engelsbel S, et al. Are gestational
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12 Frates MC, Doubilet PM, Peters HE, Benson CB. Adnexal
sonographic findings in ectopic pregnancy and their 18 Marks WM, Filly RA, Callen PW, Laing FC. The decidual
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19 Hill LM, Kislak S, Martin JG. Transvaginal sonographic
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CHAPTER 7

Incidental Findings

Joseph Minardi, MD

SECTION 1
Incidental Findings

KEY POINTS MOVIE 7.1 Key Incidental Findings

1. Common incidental findings include Key Incidental Findings.
nabothian cysts and fibroids. While point-of-care pelvic ultrasound is not meant to be
comprehensive, the sonologist should recognize common
2. Pregnancy in the setting of an IUD is an
ectopic pregnancy until proven otherwise. 78

3. Periuterine vasculature may be
distinguished from other entities using
color Doppler.

4. Normally, fallopian tubes cannot be
visualized with ultrasound.

5. Any complex ovarian cyst requires a follow
up ultrasound.

incidental uterine and adnexal findings. . In this chapter, we 4. Pregnancy occurring with an intrauterine device (IUD) in

will review some common normal variants as well as some place is an ectopic pregnancy until proven otherwise.

common abnormal, but non-emergent findings that may be Nabothian cysts
encountered. It is important that these findings are not

mistaken for pathology. Further, GALLERY 7.1 Incidental Uterine Findings Nabothian cysts are a common,
recognizing common findings normal finding in the lower
allows the clinician to create a Nabothian Cyst uterine segment and cervix of
more complete sonographic and young women. They may be
clinical picture in order to make Nabothian Cyst seen on physical inspection of
more informed treatment and the cervix as well as visualized
follow-up decisions. sonographically.(2) They are

typically small, thin walled,

circular, fluid filled cysts found

Uterine Findings (Gallery 7.1) • Located within the in the lower uterine segment
Clinical Pearls: myometrium and cervix (see nabothian 1 and
2). Nabothian cyst walls are
1. Nabothian cysts are located • Absence of a surrounding nearly invisible by ultrasound.
in the myometrial portions of the decidual layer Fluid within the cysts is typically
lower uterine segment and hypoechoic or anechoic, but
cervix, have thin walls and Transvaginal sagittal image in patient with anechoic na- more echogenic material is
typically contain simple fluid bothian cyst. sometimes present. They are
typically small, 2-4 mm in
2. Leiomyomas or fibroids are diameter, but larger cysts,
common and may be variable in measuring up to 4 cm may be
location. found. Posterior acoustic

3. Fibroids have a enhancement may be noted,

heterogeneous appearance with but may be difficult to

streaking attenuation artifacts often obscuring other appreciate with smaller cysts (see nabothian 3 and 4).(3, 4)

structures. Nabothian cysts could potentially be mistaken for a

79

gestational sac of a cervical ectopic pregnancy. Noting the characterized on ultrasound by hypoechoic areas within the
location in the myometrial portion of the uterus, the simple fibroid.(7-9)
nature of the contents and the very thin, nearly invisible walls
should allow the clinician to differentiate these cysts from The sonographic appearance of fibroids is variable, typically
ectopic pregnancy, gestational sac, or other dangerous consisting of a hypoechoic or heterogeneous mass, distorting
pathology the uterine contour. Attenuation and shadowing is common,
often making visualization of other important anatomy difficult
Leiomyomas/Fibroids (see fibroid 4). (Insert various fibroid US pics)

Leiomyomas, commonly known as fibroids, are the most Fibroids are generally benign and malignant transformation is
common uterine mass. A 1997 longitudinal study of US rare. Specific follow up is recommended only for symptomatic
nurses found fibroids occur in 8.9 per 1000 white women and lesions. Fibroids may be mistaken for other malignant lesions
30.6 per 1000 black women.(5) They are often an or possibly ectopic pregnancy and consultative ultrasound will
asymptomatic incidental finding on pelvic ultrasound. be required when the diagnosis is in doubt. However,
However, they may cause symptoms including pain and/or recalling the general high prevalence of fibroids and noting
bleeding. Their location is categorized as intramural, the typical appearance should help the clinician avoid
submucosal, or subserosal. confusion.

• Intramural - confined to the myometrium Bicornuate Uterus (Movie 7.2)

• Submucosal - project into the uterine cavity Bicornuate uterus is a uterus composed of two uterine “horns”
separated by a septum as a result of abnormal fusion in
•" Subserosal - lie on the outer borders or peritoneal embryogenesis. It is a variation of normal anatomy that
surfaces of the uterus, and may even appears as occurs in 0.4 % of women, although it is likely
pedunculated masses underestimated.(10) It is commonly referred to as a heart-
shaped uterus. While this anatomical variation was once
Submucosal fibroids may lead to problems with infertility and thought to cause infertility, recent research does not support
can increase the risk of spontaneous abortion.(6) Additionally, this.(11) These pregnancies are typically considered high risk
fibroids located in the lower uterine segment or cervix may due to the potential for increased adverse effects including
interfere with vaginal delivery.(6) Pregnant women with recurrent pregnancy failure, preterm birth, malpresentation,
fibroids may experience acute pain from degeneration
80

and fetal deformities.(12) However, patients can have a and ensuring 8 mm of myometrium surrounding the
relatively normal pregnancy course depending on the extent gestational sac.(13) Ruling out an interstitial pregnancy is
of anatomic variation and implantation site of the fetus. Due extremely important as these cases carry seven times higher
to the abnormal anatomy of the uterus, a pregnant bicornuate risk of morbidity and mortality compared to tubal ectopic
uterus can be mistaken for an interstitial ectopic as often the pregnancies.(13)

MOVIE 7.2 Bicornuate Uterus Intrauterine Device (IUD)

Bicornuate uterus. IUDs are a commonly used and highly effective form of
pregnancy will appear to be implanted off- center. Because of contraception. They consist of a T-shaped polyethylene
this possibility it is important that the practitioner make sure to frame with a copper wire or a levonorgestrel-containing collar
thoroughly sweep through the uterus and ensure that there is around the stem. Complications associated with IUD
at least 5 mm of myometrium surrounding the GS. Emergency placement include expulsion out of the cervical canal,
medicine literature suggests being even more conservative fragmentation of the IUD, displacement, uterine perforation
and infection.(14) Non-visualization of IUD strings on clinical
examination or excessive pelvic pain following recent IUD
insertion should prompt ultrasound evaluation of IUD location.
Appropriate IUD position should be recognized on ultrasound.
The long axis of the IUD stem should follow the exact path of
the endometrial canal. The arms of the IUD should extend
laterally at the fundus. Copper IUDs will be more easily
visualized on ultrasound than hormonal IUDs which have
echogenic proximal and distal ends only. (include pics).
Partial expulsion out of the cervical canal requires evaluation
by gynecology due to inefficacy of a partially expulsed IUD.
(15) Management of an asymptomatic malpositioned IUD in
the myometrium, which occurs in up to 25% of patients with
IUDs, is variable with some patients electing removal and
others deciding on observation.(16) If an IUD is not

81

visualized on ultrasound, plain films should be performed to The periuterine vasculature in females of gestational age may
rule out uterine perforation.(17) be prominent and appear very similar to ovarian follicles.
Using color Doppler may be useful to demonstrate internal
IUDs are 97-99% effective in preventing pregnancy (copper flow in the vasculature whereas ovarian follicles should not
IUD 97.5% effective versus hormonal IUD 99.5% effective).
(18) When pregnancy occurs with an IUD in place, GALLERY 7.2 Adnexal/Miscellaneous Findings
implantation is unlikely to occur in the endometrial cavity.
Therefore, these patients should be suspected of having an Hydro/Pyosalpinx
ectopic pregnancy until proven otherwise.(19)
• Fallopian tubes normally not
Adnexal/Miscellaneous Findings (Gallery 7.2) visualized
Clinical Pearls:
• Hydrosalpinx may be seen
1." Periuterine vasculature may mimic the appearance of after hysterectomy or tubal
ovarian follicles, but is less organized and color Doppler ligation
should show internal flow.
• Also seen in TOA
2." Decompressed bowel has distinctly visible alternating • Serpiginous, fluid-filled
hypoechoic and echogenic layers. Bowel filled with fluid,
stool, or air will have an irregular shape compared to ovaries structure separate from ovary
and frequently undergoes peristalsis • Can be confused with bowel

3." Hydrosalpinx and pyosalpinx consist of serpiginous fluid- Transvaginal sagittal image of left adnexa in patient with
filled structures adjacent to the ovaries and uterus without pyosalpinx. Note the dilated fallopian tube containing echo-
internal flow and are commonly seen with tubo-ovarian genic debris.
abscess.
have internal flow. The periuterine vasculature is less
Periuterine vasculature organized compared to the ovarian architecture. In addition,
ovaries typically contain visible stromal tissue and a thin oval

82

capsule. Periuterine vasculature should also be differentiated or another adnexal structure. Care should be taken when
from paraovarian and ovarian cysts. Color Doppler is useful observing the bowel as intestinal pathology may be identified
for this purpose as flow should be visible within non- including appendicitis, intussusception, colitis, and
thrombosed vessels and absent from paraovarian and ovarian constipation.(21-23)
cysts.(20)
Hydrosalpinx/Pyosalpinx
Bowel
Normally, fallopian tubes are not visualized by ultrasound.
Bowel within the female pelvis is commonly seen and can be However, if they become filled with fluid, they may be visible.
confused with normal ovaries, dilated fallopian tubes, and A fluid-filled fallopian tube is referred to as hydrosalpinx.(24)
other pathologic findings. Normal bowel, when decompressed Hydrosalpinx may be a normal finding after hysterectomy or
is made up of alternating hypo and hyperechoic layers that tubal ligation, but may also be a manifestation of tubo-ovarian
distinguish it from ovaries or other adnexal structures.(21) abscess (TOA). The appearance is that of a serpiginous,
fluid-filled structure adjacent to the uterus that is distinct from
Alternating intestinal layers from innermost to external: the ovaries. If the fluid is more echogenic or complex, this is
referred to as pyosalpinx and is even more likely to represent
•" Superficial mucosa – hyperechoic a TOA. Occasionally, blood may collect within the fallopian
tubes, which is referred to as hematosalpinx, giving the fluid a
• Deep mucosa - hyperechoic more echogenic or complex appearance as well.(25-27)
Ultrasound cannot distinguish between pyosalpinx and
• Deep mucosa/muscularis propria interface - hyperechoic hematosalpinx.

•" Muscularis propria - hypoechoic Hydrosalpinx or pyosalpinx may be mistaken for ectopic
pregnancy, paraovarian or ovarian cyst, or even normal
•" Serosa – hyperechoic structures such as bowel or vasculature. Proper identification
is aided by following the course of the structure, imaging from
When bowel becomes fluid or stool filled, the walls become at least two different planes, interrogating with color Doppler,
stretched and the layered architecture is not typically visible. and identifying the uterus and ovaries as distinct, separate
The relatively homogeneous appearance of bowel contents, structures. As always, the sonographic findings should be
as well as the irregular contours should assist in proper
identification. In addition, observing for peristalsis will confirm 83
a structure as bowel rather than ovary, dilated fallopian tube,

interpreted in the clinical context. In unclear cases, surgical Nearly all simple ovarian cysts are follicular in origin. They are
exploration may be the only means to a definitive diagnosis. one of the most common findings in pelvic ultrasound. By
definition, they are thin-walled, round or ovoid, contain simple
Ureteral Stones: hypoechoic or anechoic fluid, and display posterior acoustic

Symptomatic ureteral stones in pregnancy occurs at a rate GALLERY 7.3 Incidental Ovarian Findings
similar to that of nonpregnant women of child-bearing age.
Distal ureteral stones may be visualized during performance Simple Ovarian Cyst
of the transabdominal pelvic ultrasound examination since the
urinary bladder is visualized. The ureteral stones will be • Anechoic

echogenic and round or oval in shape. Posterior shadowing • Round or oval

may be present depending on stone composition and size. • Posterior

Ovarian Findings (Gallery 7.3) enhancement
Clinical Pearls:
Simple ovarian cysts are anechoic in appearance with poste-
1." Simple cysts are thin walled, round or ovoid containing rior enhancement and round or oval in shape
simple fluid.
enhancement.(28) Follicular cysts are simply enlargement of
2." Corpus luteal cysts have thicker, vascular walls and the normal ovarian follicles, beyond 2.5 cm.(28) They may be
occur in early pregnancy. very large and can obscure visualization of the ovarian

3." Hemorrhagic cysts have thin walls and contain some 84
internal echogenic material and always require follow-up
imaging.

4." Dermoid cysts are fat containing masses with mixed
echogenic areas and attenuation artifacts.

Follicular Cysts

parenchyma. Follicular cysts, especially larger ones, may 1. Thin, smooth walls
cause pelvic pain. Rupture of follicular cysts occasionally
causes acute pelvic pain. Follicular cysts require follow-up 2. Complex internal echoes and/or septations
only if symptomatic.
3. Typically exhibit posterior acoustic enhancement
Corpus Luteal Cysts
4. Contents do not demonstrate color Doppler flow.(28, 33,
Corpus luteal cysts are often seen in first trimester 34)
pregnancies. The corpus luteum forms during ovulation and,
when pregnancy occurs, secretes progesterone to maintain Leaked hemorrhagic contents from a ruptured hemorrhagic
endometrial growth and sustain pregnancy.(29) These cysts cyst may cause acute pain. In some cases, frank
average about 2 cm in size, regress by 10-13 weeks’ hemoperitoneum with echogenic fluid in the cul-de-sac and
gestation, and have thicker walls than follicular cysts.(30) The Morison’s pouch may be present, which can mimic a ruptured
contents may be simple, but septations and internal debris ectopic pregnancy.
are frequently present. Color flow to the rim of the corpus
luteal cyst peaks at 5 weeks’ gestational age (GA) and makes TOA and endometriomas may have a similar sonographic
differentiation from ectopic pregnancy difficult at times.(31) appearance and may not be distinguishable without other
clinical information.(35) In comparison to ectopic pregnancy,
Contextual information can assist in interpretation of the hemorrhagic cysts typically have thin walls and the internal
sonographic findings. For instance, if an intrauterine contents are disorganized and largely hypoechoic.(33)
pregnancy has been identified, a corpus luteal cyst is much Follow-up for these complex cysts is recommended in 6-12
more likely to be present than a heterotopic pregnancy. weeks or sooner depending on the clinical concerns.(36) A
Acutely presenting pregnant patients with presumed ruptured true hemorrhagic cyst should decrease in size or resolve
corpus luteal cysts require obstetric consultation and risk within this timeframe.(35) Follow-up consultative ultrasound
stratification for operative intervention.(32) is warranted for anything other than simple ovarian cysts.

Hemorrhagic Cysts Endometrioma

Hemorrhagic cysts are another common finding in pelvic Endometriomas are common benign tumors made up of
ultrasound. Hemorrhagic cysts demonstrate the following ectopic endometrial tissue that are a manifestation of
characteristics: endometriosis.(36, 37) Sonographically, they have a very
similar or nearly identical appearance to a hemorrhagic cyst.

85

The primary difference is that they do not change and may incidentally as they are usually asymptomatic.(28) They may,
even increase in size over the course of a few menstrual however, present acutely as a torsed ovary or ruptured cyst.
cycles. Clinically, endometriomas cause more indolent or
chronic pain compared to hemorrhagic cysts, which tends to Sonographically, they have a highly variable appearance that
be present more acutely. Differentiating an endometrioma usually contains prominent echogenic fatty material.(40, 41)
from a hemorrhagic cyst is difficult in the acute setting. Sebaceous material, hair, and calcified teeth may also be
Sonographic findings of pelvic inflammatory disease and TOA seen.(40) Guttman’s 1977 article describes the dermoid “tip
may also have a very similar appearance. All patients with of the iceberg sign” in which the highly echogenic cyst
hemorrhagic cysts who are able to be discharged home contents produces a bright edge with posterior attenuation
require a follow-up consultative ultrasound in 6-12 weeks.(36) that obscures other structures.(42) A dermoid plug (“dermoid
plug” sign), which is an area of echogenic material projecting
Paraovarian cysts from an ovarian cyst may also be seen.(43) Dermoid plugs
often contain calcific, dental, adipose, hair and/or sebaceous
Paraovarian cysts appear similar to follicular cysts, but are components. Dermoid cysts don’t typically exhibit internal
distinctly separate from the ovaries, often lying along the vascularity with color Doppler analysis.(40)
course of the fallopian tubes. They are thin walled, typically
round, with simple, hypoechoic or anechoic contents as well As with most adnexal masses, torsion is the most emergent
as posterior acoustic enhancement.(38) Color Doppler possible complication. The heterogeneous appearance and
should reveal no internal flow. These cysts are usually benign highly echogenic fat with attenuation artifacts should assist in
and unlikely to cause symptoms. Rarely, they may differentiating from ectopic pregnancy and other adnexal
hemorrhage, rupture, or be lead to adnexal torsion. Follow up masses. Follow-up consultative ultrasound should be
is recommended for cysts greater than 5 cm diameter in obtained for these and any other complex adnexal masses.
premenopausal women or greater than 1 cm in
postmenopausal women.(39) Ovarian Torsion

Dermoid cysts Ovarian torsion occurs when the ovary twists on its vascular
pedicle and obstructs venous return, leading to stromal
Dermoid cysts are also known as cystic teratomas. Dermoid edema, hemorrhage, and necrosis of ovarian tissue if
cysts are less commonly seen compared to the previously unrecognized. Any ovarian mass, especially larger than 5 cm,
described adnexal cysts. Often, they are recognized may increase the risk of adnexal torsion. In a 15 year
retrospective institutional study of women who underwent

86

surgery for an acute abdomen secondary to a benign ovarian References:
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•" Twisted pedicle is specific for ovarian torsion. 5 Marshall LM, Spiegelman D, Barbieri RL, et al. Variation in
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tube 967-73.

•" Free pelvic fluid 6 Navid S, Arshad S, Qurat ul A, Meo RA. Impact of
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11 Proctor JA, Haney AF. Recurrent first trimester pregnancy 18 Rowe P, Farley T, Peregoudov A, et al. Safety and efficacy
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12 Rackow BW, Arici A. Reproductive performance of women
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1389-401.
13 Lewiss RE, Shaukat NM, Saul T. The endomyometrial
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23 Timor-Tritsch IE, Lerner JP, Monteagudo A, Murphy KE, 30 Rowan K, Meagher S, Teoh M, Vollenhoven B, Choong S,
Heller DS. Transvaginal sonographic markers of tubal Tong S. Corpus luteum across the first trimester: size and
inflammatory disease. Ultrasound Obstet Gynecol. 1998 Jul; laterality as observed by ultrasound. Fertil Steril. 2008 Nov;
12(1):56-66. 90(5):1844-7.

24 Taipale P, Tarjanne H, Ylostalo P. Transvaginal sonography 31 Jarvela IY, Ruokonen A, Tekay A. Effect of rising hCG
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90

CHAPTER 8

Second/Third
Trimester Pregnancy

Kelly Gibson, MD FACOG
Justin Lappen, MD FACOG

SECTION 1
Second/Third Trimester

KEY POINTS Clinical pearls:

1. Six essential components of the second and third •" The determination of fetal presentation and lie is
trimester ultrasound examination include the essential to planning for optimal delivery and need for
determination of: fetal lie and presentation, cardiac additional resources.
activity, fetal number, amniotic fluid volume, placental
localization, and biometry. •" Placental location relative to the cervix determines the
need for cesarean section.
2. Vaginal bleeding and abdominal pain in the second and
third trimester requires timely evaluation with •" Rapid options to estimate gestational age in order to
ultrasound to guide maternal and fetal management. determine fetal viability include fundal height and femur
length.
3. Point-of-care pelvic ultrasound is part of the secondary
survey in the evaluation of the pregnant trauma Point-of-Care ultrasound (POCUS) components: 2nd/3rd
patient. trimester examination

4. Goals for point-of-care ultrasound in active labor Essential Components of Obstetric Ultrasound in the 2nd/3rd
include fetal presentation, placenta location, and fetal Trimester of Pregnancy (Movie 8.1)
viability.
1. Fetal Lie and Presentation

92

2. Fetal Cardiac Activity Fetal lie is defined as the orientation of the fetal spine relative
3. Fetal Number (singleton, twin, triplet or higher order to the maternal spine. Determination of fetal lie requires
multiple gestation) obtaining a mid-sagittal view of the fetal spine. Longitudinal
4. Amniotic Fluid Volume fetal lie occurs when the fetal and maternal spinal columns
5. Placental Localization/Placental Assessment are parallel (along the same axis), which is the most common
fetal lie in the second and third trimester. Cephalic and
MOVIE 8.1 Exam Essentials
MOVIE 8.2 Fetal Lie and Presentation

Second and third trimester ultrasound examination essen- Fetal lie and presentation
tials.
breech presentation are both examples of a longitudinal fetal
6. Fetal Biometry lie. Transverse lie occurs when the fetal spine is positioned
perpendicular to the maternal spine. When the fetal spine is
Fetal Lie and Presentation (Movie 8.2) in an oblique direction to the maternal spine (at an angle

93

between a longitudinal and transverse lie), the fetal lie is thorax and abdomen obstruct delivery through a hysterotomy
considered to be oblique. in the lower uterine segment.
Fetal Cardiac Activity (Movie 8.3)
Fetal presentation refers to which anatomical part of the fetus The determination of fetal cardiac activity is an essential
is closest to the pelvic inlet. The presentation may be
cephalic, breech, or shoulder. Determination of fetal MOVIE 8.3 Fetal Cardiac Activity
presentation is technically easier than lie, therefore we
recommend assessing fetal presentation first. A fetus in Fetal cardiac activity.
cephalic or breech presentation, by definition, has a
longitudinal lie. If the fetal head or sacrum is not visible in the component of any basic ultrasound examination. The
lower uterine segment (technique described below), then presence or absence of normal fetal cardiac activity in the
transverse or oblique lie should be suspected and a mid- second and third trimester has significant management
sagittal view of the fetal spine should be obtained to assess implications and may provide an early window into severe
the relative angle of the fetal and maternal spines. maternal or fetal pathologic processes. Furthermore, the
presence of normal cardiac activity provides an important
To determine fetal lie and presentation, place the transducer
over the maternal lower abdomen, just above the pubic
symphysis, in a transverse orientation. Angle the transducer
inferiorly toward the cervix to identify the presenting part of
the fetus (head, buttocks/sacrum, or other/none).

The determination of fetal lie and presentation are critical to
choosing the optimal mode of delivery. Attempting breech
vaginal delivery may be appropriate based on clinical factors,
experience of the health care provider, and the care setting.
(1) External cephalic version may be recommended to
women with oblique lie or breech presentation at term.
Persistent transverse lie requires cesarean delivery.
However, a classical cesarean delivery is required if the fetal
back is “down” (fetal spine in lower uterine segment) as the

94

opportunity for patient reassurance. As such, confirmation of function available on most ultrasound machines, can also be

cardiac activity should be performed early in the ultrasound used to document fetal cardiac activity and to determine the

examination. rate by detecting motion of the cardiac chambers. When M-

Documentation of fetal cardiac activity can be performed by mode is activated, a line appears on the screen which detects
motion through the tissue it intersects. The deflections on the
storing a cine-loop (video clip)
M-mode display correspond to
of the moving fetal heart or by MOVIE 8.4 Fetal Number the anatomic structures through
obtaining a static M-mode or which the M-mode line passes.
Measuring the distance
pulsed-wave Doppler image. between consecutive
deflections (ventricular
Measurement of fetal heart rate ejections, for example), can be
used to assess fetal heart rate.
can be determined by many

modalities, two of which will be

presented here. First, pulsed-

wave Doppler can be used to

calculate the fetal heart rate. Fetal Number (Movie 8.4)

Obtain a four chamber view of Multiple gestations are

the fetal heart. With the gate associated with many

width set at 3 mm, place the pregnancy complications,

Doppler gate at the level of the including preterm delivery,

mitral valve, activate the preeclampsia, abnormal labor,

Doppler signal and record the fetal malpresentation as well as

flow waveform. Place the fetal, neonatal and infant

calipers between consecutive Multiple gestations/fetal number.

ejections to calculate the fetal mortality.(3) Determination of

heart rate (R-R interval). It is important to note that some fetal number is critical to

manufactures have a 2 beat peak-to-peak calculation system. antenatal care, patient counseling, fetal surveillance, and

Concerns for heat production on developing organs by delivery planning. Given the rarity of higher order multiples,

focused Doppler waveform in the first trimester fetus are less the remainder of this section will focus on twin pregnancy

concerning in the second and third trimester.(2) M-mode, a (though similar principles and techniques apply to higher-

order multiples). On a second or third trimester ultrasound

95

examination, a twin gestation is suspected when two fetal left to right aspect of the maternal abdomen. Keep the

crania are detected. However, the presence of two separate ultrasound transducer perpendicular to the maternal abdomen

fetal bodies is necessary to confirm the diagnosis. to prevent a false diagnosis of twins, which can result from

Additionally, the overwhelming majority of twins will have a imaging the same head at various angles.

dividing membrane, indicating dichorionic-diamniotic or Amniotic Fluid Volume (Movie
8.5)
monochorionic-diamniotic
Amniotic fluid is necessary for
placentation. Less than 1% of MOVIE 8.5 Amniotic Fluid Volume normal human development
all twins are monochorionic- and may protect the fetus

monoamniotic, a subtype

without a dividing membrane.

To assess fetal number, the against mechanical trauma or

entire uterine cavity should be intrauterine infection.(4) The

assessed in a standardized, primary source of amniotic fluid

systematic manner with in the second and third

attention to the number of fetal trimester is fetal urine.

crania identified. If more than Disorders of amniotic fluid

one head is identified, volume may suggest underlying

confirmation of twins should be maternal or fetal pathology.

performed by assessing other Oligohydramnios, or decreased

body parts and evaluation for a amniotic fluid volume for a

dividing membrane. The uterine particular gestational age, can

cavity should be evaluated in Amniotic fluid volume assessment. be caused by premature rupture

two planes: transverse and of membranes, uteroplacental

sagittal. In the transverse plane, the uterus should be imaged insufficiency (hypertension,

in a superior to inferior (between uterine fundus and lower preeclampsia, and intrauterine growth restriction), postterm

uterine segment) in sequential parallel planes until the entire pregnancy or fetal genitourinary abnormalities.

cavity has been evaluated. Sequential parallel scanning Polyhydramnios, or increased amniotic fluid volume for a

should then be repeated in the sagittal orientation, from the particular gestational age, can be idiopathic (approximately

50% of cases) or related to gestational/pre-gestational

96

diabetes, fetal infection, alloimmunization, or fetal structural or To perform an AFI, the uterus is divided into four equal
chromosomal abnormalities.(4) Importantly, both quadrants, within which the deepest vertical pocket of fluid is
oligohydramnios and polyhydramnios are associated with an measured. All four measurements are then summed to
increased risk of perinatal morbidity and mortality.(5-9) generate the AFI. The technique is the same as for the MVP.
Normal AFI is gestational age dependent, however in the
Two methodologies for assessing amniotic fluid volume are second and third trimester typically ranges from 5-20 cm.(4)
commonly employed: the maximal vertical pocket (MVP) and Oligohydramnios and polyhydramnios are defined as < 5 cm
the amniotic fluid index (AFI). The techniques for both and > 20 cm respectively.(4)
methods are described below. MVP is the preferred
methodology given the simplicity of the technique and lower Placental Localization/Assessment (Movie 8.6)
false positive rate for the diagnosis of oligohydramnios, which
results in fewer obstetric interventions without an increase in Placental implantation can occur on any uterine surface:
adverse perinatal outcomes.(10) Furthermore, MVP was also anterior, posterior, lateral, fundal or overlying the internal os of
supported by a recent multidisciplinary, multi-society the cervix. The latter situation, called placenta previa,
consensus workshop.(11) represents one of the most common causes of bleeding
during the second and third trimester of pregnancy. Placenta
The MVP is defined as the measurement of the single largest previa requires a cesarean delivery. Therefore, antenatal
vertical pocket of amniotic fluid within the uterine cavity that is identification of placenta previa allows for an appropriately
free of umbilical cord or fetal parts. Amniotic fluid is anechoic planned, prelabor cesarean delivery, which is recommended
in appearance. With the transducer in the sagittal orientation at a late preterm to early term gestational age.(12)
and perpendicular to the floor, the uterine cavity should be Additionally, placenta previa (and other types of abnormal
assessed in its entirety (from left to right and from the fundus placentation, such as accreta) increase the risk of
to the lower uterine segment) to identify the single largest hemorrhage and other complications.
pocket of amniotic fluid. After identification, the pocket is
measured (in centimeters) by placing the calipers in a vertical With the transducer in sagittal orientation and perpendicular
straight line. Normal MVP ranges from 2-8 cm.(4) to the mattress or backboard/wedge, scan in parallel,
Oligohydramnios and polyhydramnios are defined as a MVP < longitudinal paths from superior to inferior (uterine fundus to
2 cm and > 8 cm respectively.(4) lower uterine segment) along the maternal abdomen from the
left to right side. Starting at the uterine fundus will ensure that
a fundal placenta will not be overlooked. Overlying fetal parts

97

may shadow and obscure a posterior placenta. Avoid this overly full urinary bladder can simulate a previa by causing
artifact by placing the transducer lateral on the maternal apposition of the anterior and posterior walls of the lower
uterine segment while an empty urinary bladder can make
MOVIE 8.6 Placental Localization/Assessment visualization of the lower uterine segment/cervical region
difficult. If the patient was experiencing a contraction during
Placental localization and assessment. the examination, the examination should be repeated after the
abdomen. After the placenta is localized, the inferior or lower contraction has resolved since the contraction can distort the
edge must be identified and the relationship of this edge to placenta and myometrium making it appear as though a
the cervix must be evaluated. A low-lying placenta occurs placenta previa is present. The diagnosis of placenta previa
when the placental edge is within 2 cm of the internal cervical should be confirmed (or ruled out) by performance of a
os but does not touch the internal cervical os. A marginal transvaginal (TV) or translabial ultrasound if the
placenta previa occurs when the placental edge touches the transabdominal (TA) ultrasound is non-diagnostic.
internal cervical os but does not cover it. A complete placenta
previa occurs when the placenta covers the internal cervical Vasa previa is assessed via a TA sagittal image of the lower
os. Ideally, the urinary bladder should be partially full since an uterine segment/cervical region with color Doppler to assess
for the presence of fetal vessels in the membranes overlying
the cervical os. Assessment of placenta accreta, increta,
percreta and abruptio placenta requires systematic TA
scanning of the placenta in both the sagittal and transverse
planes.

Fetal Biometry (Movie 8.7)

Fetal biometry refers to the anatomic measurements of the
fetus that can be used to estimate both fetal age and fetal
weight. The common biometric parameter used for estimation
of gestational age and fetal size in the second or third
trimester include: head circumference (HC), biparietal
diameter (BPD), abdominal circumference (AC) and femur
length (FL). It is important to remember that ultrasound

98

evaluation of an embryo or fetus in the first trimester (crown- gestational age but this should not be used to replace
traditional measurements when the patient is stable.
rump length through 13 6/7 weeks’ gestation) is the most
BPD and HC should be measured in a transverse section of
accurate method to determine gestational age.(13) The the head at the level of the thalami and cavum septi pellucidi.

gestational age (or estimated due date) of a pregnancy dated Other landmarks include the
midline falx and a symmetric
by first trimester ultrasonography should not be changed by appearance to the bilateral
cerebral hemispheres. The
subsequent biometric cerebellar hemispheres should
not be visible. To measure the
assessment in the second or MOVIE 8.7 Fetal Biometry BPD, activate the biometry
third trimester. Therefore, the software on the ultrasound
console and select BPD. The
earliest ultrasound in pregnancy upper caliper should be placed
on the outer edge of the
should be used for gestational proximal parietal bone and the
lower caliper should be placed
dating. When dating a on the inner edge of the distal
parietal bone. The line between
pregnancy, we recommend use the calipers should be
perpendicular to the midline
of recent guidelines supported falx.

by American Congress of The HC can be measured in the
same plane as the BPD. After selecting HC from the biometry
Obstetricians and menu, position the calipers on the two outer edges of the
proximal and distal parietal bones. The line between the
Gynecologists(ACOG), Society calipers should be perpendicular to midline falx. Open and fit
the ellipse over the contour of the fetal skull. The ellipse can
for Maternal-Fetal
99
Medicine(SMFM) and the

American Institute of Ultrasound

in Medicine(AIUM).(13)

If the goal in a critically ill Fetal biometry.
medical or surgical patient is to

determine if the fetus is

potentially viable outside of the uterus and fundal height

cannot be assessed on physical examination due to obesity, a

quick femur length or fundal height could be assessed with

ultrasound. Provided a uterine fibroid is not present, fundal

height assessment could provide a good estimate of