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Copyright Notice

Point-of-Care Obstetrical Ultrasound

The American College of Emergency Physicians (ACEP) makes every effort to ensure that contributors to its publications
are knowledgeable subject matter experts. Readers are nevertheless advised that the statements and opinions expressed
in this publication are provided as the contributors’ recommendations at the time of publication and should not be
construed as official College policy. ACEP recognizes the complexity of emergency medicine and makes no representation
that this publication serves as an authoritative resource for the prevention, diagnosis, treatment, or intervention for any
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Copyright © 2016, American College of Emergency Physicians, Dallas, Texas. All rights reserved. Except as permitted under
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ISBN: 978-0-9889973-2-5
To contact ACEP, write to PO Box 619911, Dallas TX 75261-9911; or call toll-free 800- 798-1822, or 972-550-0911.

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Funding Acknowledgement

The development of this iBook was supported by a section grant of the American College of Emergency Physicians
awarded to the ACEP Emergency Ultrasound Section.

3

Acknowledgements

Thank you ACEP, for giving me this opportunity to contribute to our dedicated point-of-care ultrasound community.  Thank
you Bob, for being my fellowship director, colleague, and friend.  And thank you to my boys Max and Garrett--for your
curiosity, patience, and boundless love.

—Jessica Goldstein

First and foremost, I want to thank my wife, Anita, and my children, Lauren and Nolan, for their tremendous patience and
never-ending support. I also want to thank Jessica for putting up with me during this project, as well as Marta Foster,
Maude Hancock, and the rest of the ACEP Educational Products team.

—Robert Jones

4

Foreword ACEP Emergency Ultrasound Section have created. This product
shows the commitment of ACEP and Emergency Medicine
leaders to bring innovative solutions to patients and medical
providers. I applaud readers for a continued commitment to the
learning of point-of-care obstetrical ultrasound.

The Point-of-Care Obstetrical Ultrasound iBook was designed Resa E. Lewiss, MD, FACEP
as a free open access medical education resource for all users.
Through the leadership of Robert Jones, DO and Jessica ACEP Emergency US Section Chair 2015-2016
Goldstein, MD, editors, this product represents an innovative Director of Point-of-Care Ultrasound
educational tool for those who care for pregnant women. University of Colorado Hospital
Aurora, CO
Obstetric ultrasound is not only a diagnostic tool, but also a
resuscitative tool.  The emergency physician and point-of care
provider can not only evaluate for the presence of pregnancy,
but also date the pregnancy, determine fetal viability, and assess
the obstetric pelvis. Ultrasound facilitates immediate and even
lifesaving management decisions.

It is hoped that this iBook will assist and encourage providers
to integrate bedside ultrasound into their practices. It is
intended to provide direct benefit to patients. The emergency
medicine community has driven the education, research, and
utilization of point-of-care obstetrical ultrasound. So it is not
surprising that this same group has written what is surely a
landmark text. Funded through a section grant of the American
College of Emergency Physicians, the iBook is one in a series
of innovative products, tools, and guides that members of the

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Preface Experts in point-of-care ultrasound from both emergency
medicine and OB/GYN have contributed to this iBook. We
The Point-of-Care Obstetrical Ultrasound iBook was developed would like to express our appreciation to the contributors for
to be a free resource for point-of-care users and to be a state- their commitment and sacrifice. We also would like to thank
of-the-art digital learning tool that can be used over a variety Courtney Smalley, MD for her invaluable assistance in peer
of bandwidths in locations all over the world. The iBook is reviewing the iBook and Lara Bohinc, RDMS for her invaluable
structured so it is easy to read, simple to follow, and practical to assistance in providing needed images for the iBook. Lastly,
use. The iBook contains numerous videos, image banks, as well we would like to thank the ACEP Ultrasound Section for its
as referenced text and can be used by both the beginner and innovation, advocacy, and commitment to advancing the global
advanced point-of-care user. It can also be used as a resource use of point-of-care ultrasound as well as the ACEP Products
for medical student, residency, and ultrasound fellowship team for supporting this project.
education.
Robert A. Jones, DO FACEP
While not meant to be a comprehensive resource on all aspects
of obstetrical ultrasound, the iBook should provide the reader Jessica Goldstein, MD FACEP
with all the didactic information required to both perform and
interpret the point-of-care OB ultrasound (POCUS) examination
on the acutely ill or injured pregnant patient. Sections cover
ultrasound scanning techniques as well as normal and key
pathologic sonographic findings encountered during the point-
of-care ultrasound examination of the acutely ill or injured
pregnant patient. For those looking for a quick reference in the
clinical setting, we have included a Bedside Consult section.

6

Contributors Department of Emergency Medicine
Ohio State University Medical Center
Robert Jones, DO FACEP Assistant Professor, Emergency Medicine
Ohio State University
Director, Emergency Ultrasound Columbus, OH
Director, Emergency Ultrasound Fellowship Abnormal Intrauterine Pregnancy
Department of Emergency Medicine
MetroHealth Medical Center Tyler Dschaak, MD
Associate Professor, Emergency Medicine
Case Western Reserve University Department of Emergency Medicine
Cleveland, OH Ohio State University Medical Center
Co-Editor Assistant Professor, Emergency Medicine
Bedside Consult 1st Trimester Ohio State University
Bedside Consult 2nd/3rd Trimester Columbus, OH
Abnormal Intrauterine Pregnancy
Jessica Goldstein, MD FACEP
Kelly Gibson, MD
Division Chief, Emergency Medicine
UH Abuja Medical Center Director, Labor and Delivery
Assistant Professor, Emergency Medicine Division of Maternal Fetal Medicine
Case Western Reserve University MetroHealth Medical Center
Cleveland, OH Assistant Professor, Obstetrics and Gynecology
Co-Editor Case Western Reserve University
Normal Intrauterine Pregnancy Cleveland, OH
Second/Third Trimester Pregnancy
Creagh Boulger, MD FACEP
Diane Gramer, RDMS, RVT, RT(R)
Associate Ultrasound Director
Ultrasound Educator
Department of Emergency Medicine
MetroHealth Medical Center
Cleveland, OH
Bedside Consult 1st Trimester
Bedside Consult 2nd/3rd Trimester

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Thompson Kehrl, MD Director, Emergency Ultrasound Fellowship
Department of Emergency Medicine
Director, Emergency Ultrasound West Virginia University Medical Center
Director, Emergency Ultrasound Fellowship Associate Professor, Emergency Medicine
Department of Emergency Medicine West Virginia University,
Wellspan York Hospital Morgantown, WV
Clinical Assistant Professor, Emergency Medicine Incidental Findings
Drexel University
York, PA Courtney Smalley, MD
Ectopic Pregnancy
Associate Staff
Melanie Kennedy, MD, MSCI Emergency Services Institute
Cleveland Clinic
Ultrasound Faculty Ultrasound Faculty
Department of Emergency Medicine MetroHealth Medical Center EMRP
Ohio State University Medical Center Cleveland, OH
Assistant Professor, Emergency Medicine Peer Reviewer
Ohio State University
Columbus, OH Matthew Tabbut, MD
Abnormal Intrauterine Pregnancy
Associate Director, Emergency Ultrasound
Justin Lappen, MD FACOG Department of Emergency Medicine
MetroHealth Medical Center
Fellow, Maternal Fetal Medicine Assistant Professor, Emergency Medicine
Department of Obstetrics and Gynecology Case Western Reserve University
MetroHealth Medical Center Cleveland, OH
Assistant Professor, Reproductive Biology Introduction
Case Western Reserve University
Cleveland, OH
Second/Third Trimester Pregnancy

Joseph Minardi, MD FACEP

Director, Emergency Ultrasound

8

CHAPTER 1

1BsetdTsriidmeeCsotenrsult

Robert Jones, DO
Diane Gramer, RDMS, RVT, RT(R)

9

Scanning Essentials • Image optimization: Place desired structure(s) in the center
of the screen and adjust the gain, time gain compensation
Clinical Indications (TGC), and focal zone(s).
• Abdominal or pelvic pain
• Vaginal Bleeding • Gel: Use an adequate amount of ultrasound gel on the
• Maternal trauma patient’s lower abdomen.
• Multiple gestations
• Fetal viability • Pelvic scanning protocol: Scan the uterus in BOTH sagittal
• Gestational dating and transverse planes.

Focused Questions • Perihepatic window: Scan the perihepatic window if no
• Is there an intrauterine pregnancy present (MAIN QUESTION)? intrauterine pregnancy found but a significant amount of
• Is the embryo or fetus viable? pelvic fluid is present.
• How far along is the embryo or fetus?
• How many embryos or fetuses are present? MOVIE 1.1:  Transabdominal Examination
• Is there free fluid present?
Transabdominal Examination
Transabdominal Examination Essentials (Movie 1.1)
• Patient position: Supine.
• Preparation: A full urinary bladder preferred, but the

examination should be attempted even if the urinary bladder
is empty.
• Transducer: 5-2 MHz transducer preferred in adult patients,
but a 5-2 MHz phased array transducer could also be used.
A high-frequency linear transducer can be used to evaluate
a gestational sac for the presence of a yolk sac when not
detected with the curvilinear transducer.(1)
• Machine setting: Use the OB/GYN preset.

10

Transabdominal Scanning Protocol (Gallery 1.1) • Transducer location: Start in midline position just cephalad to
• Transducer orientation (sagittal): The indicator is directed pubic bone.

toward the patient’s head (12 o’clock position). • Identify urinary bladder/uterus.
• Image orientation (sagittal): Head is to left of screen, foot is to • Slide transducer from side to side as needed since the uterus

the right of the screen, anterior is the top of the image, and may be tilted to the left or right.
posterior is the bottom of the image. • Apply gentle transducer pressure to improve visualization if

urinary bladder not full in order to displace bowel gas.
• Rotate/angle transducer so uterus is visualized in its long-axis.
• Sweep transducer from side to side visualizing the entire

uterus in the sagittal plane (looking for sonographic
evidence of an intrauterine pregnancy as well as abnormal
implantation).
• Assess anterior and posterior cul-de-sacs for free fluid.
• If no intrauterine pregnancy is seen, then extend sagittal
sweeps out into the adnexa.
• Sagittal to transverse scanning plane: Rotate transducer
counterclockwise 90 degrees so indicator is directed toward
the patient’s right (9 o’clock position) while centered on
uterus in sagittal plane.
• Transducer orientation (transverse): The indicator is directed
toward the patient’s right (9 o’clock position).
• Image orientation (transverse): Anterior is the top of the
image, posterior is the bottom of the image, patient’s right is
to the left of the image, and patient’s left is to the right of the
image.
• Keeping transducer perpendicular to the abdominal wall,
sweep in both cephalad and caudal directions to visualize

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entire uterus by sliding the transducer. Angling the Perihepatic Scanning Protocol (Gallery 1.2)
transducer can be utilized as needed. • Transducer: Use same curvilinear or phased array transducer.
• Apply gentle transducer pressure as needed to improve • Transducer location: Place transducer in an intercostal
visualization if urinary bladder not full.
• Assess cul-de-sacs for free fluid. oblique position between 8th and 11th ribs in the mid-
• If no intrauterine pregnancy is seen, then sweep to the left axillary line with the indicator directed toward the patient’s
and right pelvic sidewalls at the level of the uterine fundus to axilla.
evaluate the adnexa. • Image orientation: Lateral is top of image, medial is bottom
of image, head is to the left of the image, and foot is to the
right of the image.
• Rotate/angle the transducer as needed if the desired view is
not obtained.
• Identify liver, right kidney and Morison’s pouch.
• Look for hemoperitoneum in Morison’s pouch.
• Since fluid will be coming from the pelvis, move the
transducer caudally so that the tip of the liver is visualized.

Transvaginal Examination Essentials (Movie 1.2)
• Patient position: Lithotomy position is preferred. Placing

blankets or wedges under the patient’s pelvis on a regular
cart is an alternative.
• Patient preparation: An empty bladder preferred.
• A female chaperone should be present and the exam
explained to the patient.
• Transducer: An endocavitary transducer is used.
• Machine settings: OB/GYN preset should be used.
• Image optimization: Center the target structure(s) on the
screen and adjust gain, TGC, and focal zone(s).

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• Transducer preparation: Ultrasound gel is first applied to • Avoid inserting the transducer all the way into the vaginal
the transducer footprint followed by placing the transducer canal since this will potentially limit visualization.
cover and then applying sterile, water-soluble gel to the
transducer footprint. • Image orientation (sagittal): Caudal is top of image, cephalad
is bottom of image, anterior is to the left of the image, and
Transvaginal Sagittal Scanning Protocol (Gallery 1.3) posterior is to the right of the image.
• Insert transducer slowly with indicator directed toward the
• Once uterus visualized, gently rotate/angle transducer until a
ceiling (12 o’clock position) until the urinary bladder and true sagittal image of the uterus is identified.
uterus are seen.
• Transducer orientation (sagittal): Indicator is directed toward
the ceiling (12 o’clock position).

MOVIE 1.2:  Transvaginal Scanning

Transvaginal Scanning

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• Raise and lower the handle so that the entire uterus including • Sweep the handle to the left and right in order to visualize
the cervix and the cul-de-sacs are seen (the transducer may the entire uterus in the sagittal plane.
need to be pulled out slightly).
• If no intrauterine pregnancy seen, then continue to sweep
• Anteverted uterus: Raise the handle up to visualize lower laterally (both left and right) to the pelvic sidewalls in order to
uterine segment, cervix and posterior-cul-de-sac and lower visualize the adnexa.
the handle to visualize the uterine fundus.
• With the uterus visualized in a sagittal orientation, rotate the
• Retroverted uterus: Lower the handle to visualize the lower transducer 90 degrees counterclockwise to the patient’s right
uterine segment, cervix and cul-de-sac and raise the handle (9 o’clock position).
to visualize the uterine fundus.
• Transducer orientation (coronal): Indicator is directed toward
the patient’s right (9 o’clock).

• Image orientation (coronal): Caudal is top of image, cephalad
is bottom of image, patient’s right is to the left of the image,
and patient’s left is to the right of the image.

• Gently rotate/angle the transducer as needed to get a true
transverse image.

• Raise and lower the handle so that the entire uterus, cervix
and cul-de-sacs are seen.

• If no intrauterine pregnancy seen, then angle the handle
to the patient’s right to visualize the left adnexa (and to the
patient’s left to visualize the right adnexa) at the level of the
uterine fundus followed by raising the handle up and down
to sweep through the adnexa.

Normal Intrauterine Pregnancy

Gestational Sac (Gallery 1.4)
• Intradecidual sac sign is the first sonographic finding of early

pregnancy.

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• Intrauterine pregnancy confirmation requires presence of a • Appears as round or oval, anechoic structure which
yolk sac or embryo within the sac. is completely embedded within the endometrium
eccentrically.
• Usually seen by 4.5-5 weeks’ gestational age (GA) by
transvaginal exam and one week later by transabdominal • The presence of the double decidual sign favors that the sac
exam. is an early gestational sac and not a pseudogestational sac of
an ectopic pregnancy, but this sign alone should not be used
• Usually seen by serum hCG of 1000-1500 mIU/ml to confirm the presence of an intrauterine pregnancy.
(International Reference Preparation [IRP]). This is referred to
as the discriminatory zone. Yolk Sac (Gallery 1.5)
• First sonographic evidence of an intrauterine pregnancy.
• Usually seen by 5-6 weeks’ GA by transvaginal exam and one

week later by transabdominal exam.
• Usually seen by a mean sac diameter (MSD) greater than 8

mm.
• MSD measurement more helpful than serum hCG level in

determining the threshold for yolk sac visualization.
• Appears as a round, echogenic ring with a central anechoic

appearance.
• Located outside of the amniotic cavity.
• A completely echogenic yolk sac is consistent with

pregnancy failure.

Embryo (Gallery 1.6)
• Usually seen by 6 weeks’ GA by transvaginal exam and one

week later by transabdominal exam.
• Usually seen by a MSD greater than 16 mm. However, some

have suggested increasing the threshold for detection to 25
mm or greater.

15

• MSD measurement more helpful than serum hCG level in • In embryos with crown-rump length (CRL) less than 5 mm,
determining the threshold for embryonic visualization. the heart rate (HR) should be greater than 80 beats per
minute (BPM).
• Appears as an echogenic structure within the amniotic cavity.
• Embryonic cardiac activity should be identifiable when • The lower limit of normal for embryonic heart rate is 100
beats per minute up to 6.2 weeks’ GA and 120 beats per
the embryo is 5 mm in length or greater. However, some minute at 6.3-7.0 weeks’ GA.
have suggested increasing the threshold to 7 mm in length
or greater to minimize the chance of falsely diagnosing a Cul-de-sac Fluid (Gallery 1.7)
pregnancy as nonviable. • A small amount of simple fluid (anechoic) may be seen in

normal pregnancies and is termed “physiologic”.
• The volume of fluid is qualitatively described using terms

such as small, moderate, and large.
• The presence of echoes within the fluid is a cause for

concern regardless of the amount since this is suggestive
of hemorrhage in the patient with a possible ectopic
pregnancy.

Multiple Gestations (Gallery 1.8)
• The chorionicity and amnionicity of a multiple pregnancy

should be determined, if possible
• Dichorionic twins will be diamniotic.
• Amnionicity of monochorionic twins is based on the number

of yolk sacs present.
• Dichorionic/diamnionic twin gestations occur in @25% of

cases.
• Monochorionic/diamnionic twin gestations occur in @75% of

cases.
• Monochorionic/monoamniotic twin gestations occur in @1%

of cases.

16

• The twin closest to the cervix should be labeled twin A and Pregnancy Dating
one closest to the fundus should be labeled twin B.
Mean Sac Diameter (MSD)
• A subchorionic hemorrhage can be confused with the • Performed when gestational sac is visualized but embryo is
gestational sac of a twin pregnancy.
not.
• Accurate to within 5-7 days’ GA.
• Performed by taking 3 measurements (length, width, and

height) of the gestational sac using sagittal and transverse
images of the uterus.

17

Crown-rump Length (CRL) Gestational Trophoblastic Disease (Gallery 1.10)
• Performed once the embryo is visualized.
• Accurate to within 5-7 days’ GA. • A complete mole will appear as a large, complex mass within
• The yolk sac should not be included in this measurement. the endometrial cavity with multiple small cystic spaces
• Biparietal Diameter (BPD) is more accurate by the end of the surrounded by echogenic tissue (the “cluster of grapes”
appearance).
first trimester since fetal flexion and extension will result in
inaccuracies in the CRL measurement. • Classic sonographic findings are more common in the
second trimester.
Pregnancy Failure (Gallery 1.9)
• A partial mole is a form of disease in which both a fetus and
• Term used to describe early pregnancy nonviability. abnormal trophoblastic tissue are present. Commonly, the
• Other terms, such as anembryonic pregnancy, intrauterine fetus has an abnormal sonographic appearance.

fetal demise, and blighted ovum can be confusing and Partial vs. Complete Miscarriage
should be avoided.
• Current controversy surrounding the sonographic • The sonographic findings associated with retained products
discriminatory zones. of conception (RPOC) include a thickened endometrium with
• Definitive evidence based on current criteria includes the echogenic material present, but this is a non-specific finding.
presence of an embryo greater than 5 mm in length without
cardiac activity (Proposed criteria uses embryo greater than 7 • Definitive findings include the presence of placental or fetal
mm in length without cardiac activity). tissue.
• Possible findings include: abnormal gestational sacs features,
a MSD greater than 8 mm with no yolk sac visualized, or • Color Doppler can be used to identify feeding vessels
a MSD greater than 16 mm with no embryo visualized associated with RPOC.
(Proposed criteria uses MSD greater than 25 mm with no
embryo visualized). • The diagnosis of a completed miscarriage cannot be made
• In cases of possible pregnancy failure, it is always best to give with certainty just by the ultrasound findings alone (need
the pregnancy the benefit of the doubt and recommend a to correlate with history and physical exam findings). If a
follow up ultrasound and repeat serum hCG level. prior ultrasound confirming an IUP or definitive evidence of
passage of an IUP are not available, one should be careful in
interpreting the findings of a normal ultrasound.

18

Ectopic Pregnancy (Gallery 1.11) Cervical Ectopic
• Sonographically, implantation will be visualized in the
Anatomic Locations
• Fallopian tube- @95% cervical region.
• Interstitial- @2-4% • The presence of cardiac activity strongly suggests a cervical
• Ovary- @0.5%
• Cervix- @0.1% ectopic, while an abnormal sac with a nonviable embryo
• Abdominal- @0.03% suggests the cervical phase of a spontaneous miscarriage.
• Serial scans are recommended if the diagnosis remains in
Endometrial Findings doubt after ultrasound examination.
• Trilaminar appearance is specific but not sensitive for the
Abdominal Ectopic
diagnosis of ectopic pregnancy. • Ultrasound will demonstrate a fetus within the peritoneal
• Pseudogestational sacs are seen in @10 percent of ectopic
cavity.
pregnancies. • These are exceeding rare.
• Most commonly found in the posterior cul-de-sac or
Tubal Ectopic
• Definitive sonographic findings include the identification of a adjacent to the fundus of the uterus.

gestational sac containing an embryo or yolk sac. Heterotopic Pregnancy
• Nonspecific findings include adnexal (tubal) ring, complex • Heterotopic pregnancies are more common in patients who

mass and free fluid. have undergone assisted reproduction than in the general
population.
Interstitial Ectopic • In patients who have undergone assisted reproduction,
• Sonographic findings include an empty uterine cavity with a expect unusual combinations including multiple IUPs and
multiple extrauterine pregnancies.
chorionic sac < 5 mm from the myometrial border. • In a patient who has undergone assisted reproduction, the
• Uterine contractions resulting in an eccentrically located but adnexal, cervical, and cornual regions must be scanned even
if an intrauterine pregnancy is found.
normally implanted uterine sac, an early IUP in a bicornuate
uterus, and a uterine fibroid in a pregnant patient without a
visualized IUP can all be mistaken for an interstitial ectopic
pregnancy.

19

References:

1. Tabbut M, Harper D, Gramer D, Jones R. High-frequency linear
transducer improves detection of an intrauterine pregnancy in first-
trimester ultrasonography. Am J Emerg Med. 2016;34(2):288-291.

20

CHAPTER 2

B2nedds/3idred CTroinmseusltter

Robert Jones, DO
Diane Gramer, RDMS, RVT, RT(R)

21

Scanning Essentials • Machine setting: Use the OB/GYN preset.
• Gel: Use an adequate amount of ultrasound gel.
Clinical Indications • Image optimization: Place desired structure(s) in center of
• Abdominal or pelvic pain
• Vaginal bleeding screen and adjust gain, TGC, and focal zone(s).
• Maternal trauma • Pelvic scanning protocol: The uterus is scanned in BOTH
• Maternal critical illness
• Fetal number sagittal and transverse planes.
• Fetal viability • eFAST scanning protocol: Performed in cases of maternal
• Fetal presentation
• Gestational dating trauma.
• Placental localization
Transabdominal Scanning Protocol
Focused Questions • Fetal lie and presentation
• How many fetuses are present? • Fetal cardiac activity
• Is the fetus viable? • Fetal number
• How far along is the fetus? • Amniotic fluid volume
• Where is the placenta located? • Placental localization
• What is the fetal presentation/lie? • Fetal biometry
• Is there sonographic evidence of hemoperitoneum/
Sonographic Findings
hemopericardium/pneumothorax (maternal trauma)?
Fetal Lie and Presentation (Gallery 2.1)
Transabdominal Examination Essentials • Fetal lie and orientation of the fetal spine relative to the
• Patient position: Supine (with wedge under patient’s right
maternal spine.
side to displace the uterus off of the inferior vena cava). • Determination requires obtaining a mid-sagittal view of the
• Preparation: None.
• Transducer: 5-2 MHz curvilinear probe preferred in adult fetal spine.
• Fetal lie: longitudinal (fetal and maternal spines parallel),
patients, but a phased array probe of similar frequency could
also be used. transverse (fetal spine is perpendicular to the maternal spine),
and oblique (angle between longitudinal and horizontal).
• Fetal presentation refers to which anatomic part of the fetus
is closest to the pelvic inlet (cephalic, breech, or shoulder).

22

• Fetus in cephalic or breech presentation has a longitudinal • Polyhydramnios is defined as MVP > 8 cm.
lie.
Placental Localization/Assessment (Gallery 2.4)
Fetal Cardiac Activity • Identification of placenta previa essential since these patients
• Presence or absence has significant management
require C-section.
implications. • Low-lying placenta previa: edge within 2 cm of cervical os
• Can be calculated using M-mode or pulsed-wave Doppler
but does not touch the internal cervical os.
(M-mode preferred). • Marginal placenta previa: edge touches the internal cervical

Fetal Number (Gallery 2.2) os but does not cover it.
• Multiple gestations associated with numerous pregnancy • Complete placenta previa: placenta covers the internal

complications. cervical os.
• Determination of fetal number requires scanning the entire • A full urinary bladder or focal myometrial contractions may

uterine cavity in a systematic fashion with attention to the make the placenta appear closer to the internal cervical os
number of fetal crania. than it really is so rescan the patient with bladder empty or
• Look for a dividing membrane which indicates a diamniotic after contraction ends if placenta previa is questioned.
pregnancy (Di-Di or Mono-Di). • Transvaginal ultrasound should be used to confirm
questionable placenta previa seen on transabdominal
Amniotic Fluid Volume (Gallery 2.3) ultrasound.
• Primary source of amniotic fluid in the 2nd/3rd trimester is • Vasa previa refers to the presence of fetal blood vessels
between the presenting fetal parts and the cervix and is
fetal urine. associated with significant perinatal mortality.
• Oligohydramnios and polyhydramnios are both associated • Abruptio placenta: sonographic findings include the
presence of a retroplacental clot but it is essential to
with and increased risk of perinatal morbidity and mortality. understand that the sensitivity of ultrasound in the detection
• Maximal vertical pocket (MVP) and amniotic fluid index (AFI) of abruptio placenta is low and therefore cannot exclude the
diagnosis.
are the two methods for assessing amniotic fluid volume
(MVP is the preferred method due to simplicity and lower 23
false positive rate for oligohydramnios).
• Normal MVP ranges from 2-8 cm.
• Oligohydramnios is defined as MVP < 2 cm.

Fetal Biometry (Gallery 2.5)
• Head circumference and biparietal diameter: measured in a

transverse section of the head at the level of the thalami and
cavum septi pellucidi.
• Abdominal circumference: symmetrical, circular transverse
section of the fetal abdomen that includes visualization of
the vertebrae in cross section, the stomach bubble, and
intrahepatic umbilical vein with portal sinus.
• Femur length: measured in full length of the bone
perpendicular to the ultrasound beam EXCLUDING the
epiphysis.
• Each measurement has its own pros and cons.
NOTE: The best measurement in the critical setting is the one
that can be obtained the easiest (and most accurately).

24

CHAPTER 3

Introduction

Matthew Tabbut, MD

25

SECTION 1

Introduction

KEY POINTS Role of ultrasound in pregnancy

1. Ultrasound plays an integral role in the evaluation of the It is estimated that over 211 million pregnancies occur every
pregnant patient. year worldwide with pregnancy complications being the
leading cause of mortality among women of childbearing
2. Point-of-care ultrasound enhances the bedside evaluation years.(1) In 2015 over 300,000 women died of pregnancy
of the pregnant patient. related complications with a maternal mortality rate
worldwide equaling approximately 200 maternal deaths per
3. Point-of-care ultrasound examinations are focused studies 100,000 live births. Countries of impoverished economic
designed to answer specific clinical questions. means are disparately affected, most notably Sub-Saharan
Africa. In developed countries, mortality has fallen over the
4. Point-of-care ultrasound is not meant to replace last half century to approximately 12 maternal deaths per
comprehensive ultrasound imaging. 100,000 live births.(2) This decrease is believed to be in part
due to the use of ultrasound in prenatal care.(3, 4) The World
Health Organization lists hemorrhage, infection and elevated
blood pressure as some the common causes of maternal
mortality. While the availability and sophistication of care
is different in the developed world, many of the causes of

26

mortality are similar.(5) Ultrasound has revolutionized the of ultrasound has been brought to the bedside and is now
medical care provided during pregnancy both as a screening being performed and interpreted by the clinical physician at
tool for pregnancy and fetal complications in the evaluation of the “point-of-care”, thus allowing for a seamless integration
the acutely ill or injured pregnant patient as well as in routine of clinical and imaging findings. This shift to point-of-care
prenatal care. ultrasound (POCUS) has brought the diagnostic ability of
ultrasound from the imaging suite (which may be separated
Ultrasound in the uncomplicated pregnancy is traditionally from patient care by time, distance or physical interaction)
performed at planned intervals for the purpose of fetal to the bedside and has empowered clinical physicians to
evaluation and monitoring. In the first trimester, ultrasound is incorporate imaging findings to patient care in real time.
used primarily for gestational localization as well as screening
for fetal age, multiple gestation and aneuploidy. In the second The concept of POCUS, however, differs from traditional imaging
trimester, ultrasound is used to assess fetal and placental in its scope. Whereas traditional imaging is performed and
development. In the third trimester, ultrasound is used to evaluated by imaging specialists who are trained to perform
further monitor fetal development, for delivery planning and studies and analyze images in a comprehensive manner; POCUS
screening for potential complications of delivery. However is by definition a limited study, focused on an organ system
when the pregnant patient is acutely injured or ill, rapid or specific area of concern which seeks to answer focused
assessment includes ultrasound to assess for fetal location, questions pertinent to patient care. Clinicians throughout the
viability and pregnancy related complications as well as non- house of medicine use POCUS at the bedside to assist with their
pregnancy related pathology. clinical exam and diagnostic assessment.(6)

Ultrasound at the bedside When evaluating the acutely ill or injured pregnant patient,
often the clinical exam is of limited utility and fetal imaging is
Traditionally ultrasound has been performed in a necessary. POCUS is extremely valuable in answering specific
comprehensive manner in specific imaging suites. Similar to questions related to the patient condition (i.e. Is there an intra-
other modalities, ultrasound imaging is typically performed uterine or ectopic pregnancy? What is the fetal heart rate?
and interpreted by physicians specializing in imaging who What is the gestational age? Is there free fluid? Where is the
may not be directly involved in clinically assessing or caring for placenta? Is the fetus vertex or breach?) Ultrasound has been
the patient. However as developing technology has allowed shown to be useful in the hands of clinical physicians to rapidly
for smaller and more portable ultrasound machines, the use identify normal pregnancy, diagnose obstetric emergencies,

27

and guide management especially in the first trimester.(7- acute findings. Since the goal of POCUS is to answer specific
11) Additionally it has been shown to provide results more and pertinent clinical questions, pregnant women must still
rapidly than consultative ultrasound.(12, 13) As such, the use undergo traditional, comprehensive prenatal ultrasound
of point-of-care ultrasound has become an integral part of the surveillance. Additionally, since POCUS can yield uncertain,
evaluation of the pregnant patient presenting with variety of indeterminate or unexpected findings, these patients often
acute complaints. require referral for comprehensive fetal diagnostic imaging.

Point-of-care ultrasound in the pregnant patient is not In summary, modern obstetrical care relies heavily on
intended to obviate the need for comprehensive sonography. ultrasound in the routine evaluation of the uncomplicated
Understanding the limitations of POCUS is important for the pregnancy and the management of the acutely ill or injured
physician using ultrasound in the bedside evaluation of patients. pregnant patient. While there remains a role for comprehensive
imaging, POCUS enhances the evaluation and management of
Despite the benefits to performing and interpreting pregnant patients by interpreting ultrasound findings within
ultrasound imaging at the bedside, ultrasound acquisition the clinical context at the bedside to answer pertinent clinical
and interpretation is more operator dependent than other questions.
imaging modalities such as X-ray, computed tomography (CT)
or magnetic resonance imaging (MRI). The performance and References:
interpretation of POCUS is often limited by the practitioner’s
training, skill and clinical perspective. 1. Van Lerberghe W, editor. Facts and Figures from the World Health
Report 2005. Geneva, Switzerland: World Health Organization Press;
While POCUS is useful in answering pertinent clinical questions, 2005.
the list of differential diagnoses of concern to the physician
caring for the acutely ill or injured pregnant patient does 2. Alkema L, Chou D, Hogan D, et al. Global, regional, and national
not reflect the entirety of pathologies that can adversely levels and trends in maternal mortality between 1990 and 2015,
affect pregnant women or fetuses (i.e. malignancies, adnexal with scenario-based projections to 2030: a systematic analysis by
pathology, congenital fetal anomalies, etc.). Traditional the UN Maternal Mortality Estimation Inter-Agency Group. Lancet.
imaging specialists such as radiology or obstetrics perform 2016 Jan 30;387(10017):462-74.
comprehensive imaging studies that look for features of an
expanded differential diagnosis consisting of acute and non- 3. Harris RD, Marks WM. Compact ultrasound for improving maternal
and perinatal care in low-resource settings: review of the potential
benefits, implementation challenges, and public health issues. J
Ultrasound Med. 2009 Aug;28(8):1067-76.

28

4. Akinmoladun JA, Ogbole GI, Lawal TA, Adesina OA. Routine prenatal 12. Blaivas M, Sierzenski P, Plecque D, Lambert M. Do emergency
ultrasound anomaly screening program in a Nigerian university physicians save time when locating a live intrauterine pregnancy
hospital: Redefining obstetrics practice in a developing African with bedside ultrasonography? Acad Emerg Med. 2000
country. Niger Med J. 2015 Jul-Aug;56(4):263-7. Sep;7(9):988-93.

5. Creanga AA, Berg CJ, Syverson C, Seed K, Bruce FC, Callaghan WM. 13. Shih CH. Effect of emergency physician-performed pelvic
Pregnancy-related mortality in the United States, 2006-2010. Obstet sonography on length of stay in the emergency department. Ann
Gynecol. 2015 Jan;125(1):5-12. Emerg Med. 1997 Mar;29(3):348-51; discussion 52.

6. Moore C, Todd WM, O’Brien E, Lin H. Free fluid in Morison’s pouch 29
on bedside ultrasound predicts need for operative intervention
in suspected ectopic pregnancy. Acad Emerg Med. 2007
Aug;14(8):755-8.

7. McRae A, Murray H, Edmonds M. Diagnostic accuracy and clinical
utility of emergency department targeted ultrasonography in the
evaluation of first-trimester pelvic pain and bleeding: a systematic
review. CJEM. 2009 Jul;11(4):355-64.

8. Saul T, Lewiss RE, Rivera Mdel R. Accuracy of emergency physician
performed bedside ultrasound in determining gestational age in
first trimester pregnancy. Crit Ultrasound J. 2012;4(1):22.

9. Stein JC, Wang R, Adler N, et al. Emergency physician
ultrasonography for evaluating patients at risk for ectopic
pregnancy: a meta-analysis. Ann Emerg Med. 2010 Dec;56(6):674-
83.

10. Adhikari S, Blaivas M, Lyon M. Diagnosis and management of
ectopic pregnancy using bedside transvaginal ultrasonography in
the ED: a 2-year experience. Am J Emerg Med. 2007 Jul;25(6):591-6.

11. Bailey C, Carnell J, Vahidnia F, et al. Accuracy of emergency
physicians using ultrasound measurement of crown-rump length
to estimate gestational age in pregnant females. Am J Emerg Med.
2012 Oct;30(8):1627-9.

CHAPTER 4

NProergmnaalnIcnytrauterine

Jessica Goldstein, MD

30

SECTION 1

Normal Intrauterine Pregnancy

KEY POINTS Embryosonology

1. Gestational age starts with the first day of the last menstrual Gestational Dating Terminology
period (FDLMP). The first trimester of pregnancy spans thirteen weeks
from the first day of a woman’s last menstrual period
2. The yolk sac is the first reliable sign of an intrauterine (FDLMP). Conception occurs approximately two weeks
pregnancy (IUP). following the FDLMP. Clinicians use gestational age (GA) to
measure the developmental age of the embryo and fetus,
3. Crown-rump length is accurate to within 5-7 days while embryologists use fertilization age to measure the
gestational age (GA). developmental age of the embryo and fetus. GA begins with
the FDLMP. All dates presented in this iBook will be in GA.
4. The presence of a gestational sac does not definitively
diagnose the presence of an intrauterine pregnancy (IUP). Embryologic Periods of the First Trimester (Gallery 4.1)
• Ovarian period—the first 1-2 weeks’ GA
• Conceptus period—the 3-5 weeks’ GA
• Embryonic period—the 6-10 weeks’ GA
• Fetal period—the 11-12 weeks’ GA

31

Ovulation • A GS is a round or ovoid structure embedded in the decidua
Ovulation occurs at approximately 14 days after the FDLMP. It in the mid to upper 1/3 of the uterine fundus.
is during ovulation that the maturing follicle releases the egg
(oocyte) along with follicular fluid into the peritoneal cavity. The • A pseudogestational sac of an ectopic pregnancy may be
oocyte enters the fallopian tube and makes its way towards the confused for an early GS.
waiting sperm. If the oocyte is not fertilized, the corpus luteum
involutes. • The discriminatory zone for detection of a GS is
approximately 1000 -1500 mIU/ml (International Reference
Fertilization/Implantation Preparation [IRP]) via transvaginal (TV) ultrasound; however
Fertilization occurs when the sperm and oocyte unite to form an hCG level below the threshold should not dissuade
the zygote in the outer third of the fallopian tube (Figure). The the clinician from ordering an ultrasound if an abnormal
zygote undergoes cellular division as it travels through the pregnancy is suspected.
fallopian tube and by approximately 17 days’ GA reaches the
uterus.(1) The zygote has matured into the blastocyst stage by Two sonographic signs of early pregnancy, the intradecidual
the time it is ready for implantation at approximately 20-21 days’ sign and the double decidual sign, were defined in the 1980s,
GA.(1) The implantation process is completed by approximately prior to the widespread use of TV ultrasound.(2,3) These signs
23 days’ GA and embryogenesis continues.(1) However, it is were first described as a method of differentiation between
not until 4.5 to 5 weeks’ GA that the first reliable sonographic an early IUP and the pseudogestational sac of an ectopic
evidence of an intrauterine pregnancy (IUP) is visualized. pregnancy. A recent study found that these signs were absent
in at least 35% of GS when current TV sonographic technology
Gestational Sac (Movie 4.1) was used and that interobserver variability in interpreting these
signs was high.(4)
Clinical Pearls:
• A gestational sac (GS) is the first visible sonographic sign of The intradecidual sac sign consists of a circular, anechoic
structure measuring only a few millimeters which is completely
an intrauterine pregnancy (IUP). embedded within the endometrium, abuts the endometrial
• IUP confirmation requires the presence of a yolk sac or stripe, and does not deform the midline endometrial stripe.
It is usually seen by 4.5 weeks’ GA by TV ultrasound.(2) This
embryo within the sac. finding is unfortunately neither sensitive nor specific enough to
definitively diagnose the presence of an IUP.

32

The double decidual sac sign is seen as two echogenic rings stripe while early gestational sacs will abut against the
surrounding the anechoic gestational sac (Gallery 4.2). The endometrial stripe.
outer ring is formed by decidua parietalis (also called vera) and
the inner ring is formed by decidua capsularis. It is usually seen Yolk Sac (Movie 4.2)
by 5.5 weeks’ GA by TV ultrasound which is about the same
time the YS is seen.(3) This sign had more significance prior to Clinical Pearls:
the widespread availability of transvaginal ultrasound when the • The yolk sac is the first reliable sign of an IUP.
interval between GS and YS visualization on TA scanning was • The yolk sac is usually seen by 5.5 weeks’ GA by TV ultrasound.
longer. This finding is also neither sensitive nor specific enough • Sonographically appears as a round, echogenic ring with a
to definitively diagnose the presence of an IUP and should be
interpreted with caution. central anechoic appearance.
• The yolk sac is usually seen with TV ultrasound when the
The differential for an intrauterine sac includes 1) a
pseudogestational sac of an ectopic pregnancy and 2) a mean sac diameter (MSD) is 8 mm.
decidual cyst. Pseudogestational sacs, once reported as The first reliable sign of an IUP is the yolk sac which is visible
occurring in 20% of ectopic pregnancies, have more recently by about 5.5 weeks’ GA with TV ultrasound.(11) The yolk sac
been estimated in 5-10% of ectopic pregnancies.(5-8) A provides nutrition to the growing embryo until the placental
pseudogestational sac is thought to result from decidualization circulation takes over. As the umbilical cord and placenta grow,
of the endometrium from hormones produced by an ectopic the yolk sac becomes obsolete and is no longer visible at about
pregnancy. Pseudogestational sacs have low sensitivity and 12 weeks’ GA.(12) Initially, the yolk sac appears as a round,
varying reported specificity for ectopic pregnant.(6,9) Benson echogenic ring located eccentrically within the gestational
et al. reported that fluid can be seen in the uterus in 16.6% of sac. The clinical significance of an irregular yolk sac shape
patients with ectopic pregnancy but concluded that in the with wrinkled margins or indented walls is not known and is
vast majority of cases, it can be distinguished from an early controversial.(13) The threshold for sonographic visualization
intrauterine gestational sac based on shape, contents, and/ of the yolk sac is best made from the mean sac diameter (MSD)
or location.(10) Decidual cysts represent areas of decidual measurement and not the hCG level. The yolk sac should be
breakdown and tend to be located away from the endometrial visible when the MSD of the GS is 8 mm by TV ultrasound;
however, the yolk sac may appear later as the MSD approaches
20 mm so one needs to be cautious when interpreting these
numbers.(4,14) Absence of a yolk sac when the MSD is 16-24

33

mm is highly suspicious for pregnancy failure.(4) The upper Fetal Heart Rate (FHR)
limit of the yolk sac diameter between 5-10 weeks GA is about Embryonic cardiac activity is usually seen by approximately
5-6 mm and it has been generally accepted that an abnormally 6 weeks’ GA with TV ultrasound. In an in-vitro fertilization lab
large yolk sac indicates a poor obstetrical outcome.(13,15,16) population, which differs from an Emergency Department
The absence of a yolk sac in the presence of an embryo is patient population, fetal cardiac activity at 6 weeks’ GA has a
always abnormal. The controversy surrounding the threshold 93% positive predictive value of completing the first trimester.
values for detection of yolk sac will be discussed in greater detail (17) With improved ultrasound technology, embryonic cardiac
in the Pregnancy Failure and Ectopic Pregnancy sections of this activity can be seen as early as a crown-rump length (CRL) of
iBook. 2 mm. When embryonic cardiac activity is first visualized, the
heart rate is usually around 100-120 beats per minute (BPM).
Fetal Pole/Embryo (Movie 4.3) A study by Doubilet and colleagues concluded that the lower
limit of normal is 100 BPM up to 6.2 weeks’ GA and 120 BPM at
Clinical Pearls: 6.3-7.0 weeks’ GA.(18) The FHR plateaus after 9 weeks’ GA and
• With TV scanning, the embryo is visible by 6 weeks’ GA. the normal FHR ranges from 120-160 BPM with varying means
• Cardiac activity should be visible when the embryo is 5 mm reported, independent of gender.(19,20)

in length (crown-rump length). Cardiac activity should be visible when the CRL is 5 mm by
• At 10 weeks’ GA, the embryo is called a fetus. TV ultrasound, although some have suggested increasing the
The fetal pole is the developing embryo. It first appears as an threshold criteria to 7 mm by TV ultrasound in order to minimize
echogenic speck on the yolk sac which resembles a diamond the false-positive diagnosis of pregnancy failure.(14,21) The
ring. The embryo starts to fold and pinches off the roof of FHR is measured using M-mode. While Doppler can be used
the yolk sac to form the embryonic mid-gut. A portion of to measure embryonic or fetal cardiac activity during the first
the posterior yolk sac differentiates into the allantois which trimester, M-mode focuses lower energy than Doppler on the
eventually becomes the umbilical cord. At about 6 weeks’ GA, developing embryo and therefore M-mode is the preferred
the embryo and yolk sac are suspended within the gestational measurement tool.
sac by the allantois. At this point, the embryo appears as a grain
of rice and is normally visible with transvaginal ultrasound when 34
its length is 2-4 mm. After 10 weeks’ GA, the embryo is called a
fetus.

Amnion • Dichorionicity confers the greatest survival for twin
pregnancies.
Clinical Pearls:
• The amnion expands around the developing embryo. • The chorionicity and amnionicity of a multiple pregnancy
• The amnion is visible when the CRL is 2 mm. should be documented as early as possible.
• The amnion fuses with the chorionic cavity at 14-16 weeks’
• In monochorionic twins, amnionicity is based on the number
GA. of yolk sacs present.

The amnion derives from the inner cell mass and expands The rate of twin pregnancies in the US has climbed since the
around the embryo as it develops. Though the amnion develops 1980s due to increased maternal age and assisted reproductive
prior to the yolk sac, it is not visualized by ultrasound until after technology. The latest statistics from the National Vital Statistics
the yolk sac develops and the embryo starts to enlarge. The Report of 2013 report the incidence of twin pregnancies
amnion is visible when the CRL is about 2 mm.(2) The amnion of 33.9/1000 live births and triplet and higher pregnancies
grows like a balloon around the developing embryo and 113.5/100,000 live births.(22) The frequency of spontaneous
provides a fluid buffer between the fetus and the uterus. The monozygotic (MZ) twins remains constant across populations
amnion is always separate from the yolk sac. At approximately at approximately 3/1000 live births whereas the rates of
14-16 weeks’ GA, the amniotic cavity fuses with the chorionic spontaneous dizygotic (DZ) twins varies by numerous factors
cavity. including geography, maternal age, and socioeconomic factors.
(23-30)

Multiple Gestations (Movie 4.4) Dichorionic
Abbreviations used to describe the type of twin pregnancy refer
Clinical Pearls: to the chorionicity (monochorionic versus dichorionic) and the
• Dizygotic (fraternal) twins always have separate chorion, yolk amnionicity (monoamniotic versus diamniotic). Chorionicity
determines the likelihood of twin fetal survival with dichorionic
sacs, amnion and placenta. pregnancy conferring the best outcomes.
• Monozygotic (identical) twins may have separate chorionic
Dizygotic
sacs (dichorionic) or they may share a chorionic sac Dizygotic twins are always dichorionic, diamniotic (Di-Di).
(monochorionic) depending on when embryonic separation
occurs.

35

Monozygotic seen, the pregnancy is Mono-Di. The embryos will have one
Chorionicity of monozygotic twins depends on the timing chorion and placenta, but separate yolk sacs and amnions.
of separation of the fertilized egg. Monozygotic dichorionic, On ultrasound, look for one gestational sac and 2 yolk sacs. If
diamniotic (Di-Di) twins occur when the inner cell mass of the the amniotic sacs can be seen, they will have a thin dividing
blastocyst splits into two completely separate blastocysts less membrane. Twin- to-twin transfusion is a risk that occurs in
than 4-days post conception. When the blastocysts implant 10-15% of Mono-Di pregnancies when two embryos share
at completely different sites, they have separate chorion, yolk one placenta and more blood flow is directed to one of the
sacs, amnion and placenta. If the blastocysts implant closely, embryos.(32)
the chorions may fuse, but the vascular supply to each embryo
remains separate. About 25-30% of spontaneous identical twins Much less common in monozygotic twins and in conjoined
are Di-Di.(31) twins, the inner cell mass separates late (> 8 days post
conception) or incompletely and the embryos share a chorion,
In first trimester scans, look for two thick walled chorionic yolk sac, amnion, and placenta (monochorionic, monoamniotic
sacs and two separate yolk sacs. Do not confuse the or Mono-Mono). Mono-Mono pregnancies are described in rare
rhombencephalon of the developing fetal brain for a second case reports and are frequently complicated by umbilical cord
yolk sac. At 11-14 weeks’ GA, look for the twin peak sign, which entanglement.(33,34) Conjoined twins are even rarer.
is a projection of placental tissue extending between the two
adjacent chorionic sacs. Partial fusion of the placenta and “Vanishing twin” occurs when an embryo that was identified on
chorion is common in dichorionic pregnancies and does not an early pregnancy ultrasound disappears on a later ultrasound.
lead to twin-to-twin transfusion. Vanishing twin occurs more frequently in monochorionic
pregnancies than dichorionic (8.3% vs 2.6%).(35)
Monochorionic
The most common type of identical twin pregnancy, occurring It is important to document the number of chorionic sacs, yolk
in about 70-75% of spontaneous monozygotic twins, is sacs, and embryos as early as possible so that the risks of fetal
monochorionic, diamniotic (Mono-Di).(31) This twin pregnancy morbidity are known and can be monitored closely. In a 2014
occurs when the inner cell mass splits between 4-8 days after twin study with highly trained sonographers, the chorionicity
conception. In monochorionic twins, amnionicity is based of the twins was misdiagnosed in 6.4% of pregnancies scanned
on the number of yolk sacs present. If there are two yolk sacs prior to 20 weeks.(36) The first trimester is the best time to

36

determine chorionicity so the point-of-care user should include Gestational Dating (Movie 4.6)
this information on reports when possible.
Clinical Pearls:
Free fluid (Movie 4.5) • First trimester dating is the most reliable period for

Clinical Pearls: estimating GA.
• Physiologic free fluid is small in volume and echo-free. • CRL is accurate to within 5-7 days’ GA.
• Echogenic fluid should be assumed to be blood until proven • Use m-mode to calculate FHR.
• When the CRL is 5 mm, FHR should be > 100 BPM.
otherwise in the clinical context of suspected hemorrhage.
• Ultrasound cannot differentiate between purulent debris and Mean Sac Diameter (MSD) of the gestational sac is accurate
to within 5-7 days’ GA. Depending on the machine, the
hemorrhage when echogenic fluid is present. measurement will be the average of three orthogonally
oriented diameters in the AP and sagittal planes or just one
Physiologic fluid is often seen in pregnant and non-pregnant diameter with the assumption the sac is round. A standardized
females. Fluid visualized in the lower uterine segment of the calculation package will estimate the age based on the MSD. A
posterior cul-de-sac is considered a small volume. A moderate yolk sac will usually be seen with TV scanning when the MSD
volume of fluid extends beyond the lower uterine segment. A is 8 mm or greater and an embryo when the MSD is 16 mm or
large volume of fluid would potentially surround the uterus greater. Patients must be followed closely with serial hCG levels
extending into the anterior cul-de-sac and possibly to Morison’s and ultrasound when expected embryologic developments are
pouch in the right upper quadrant. not seen. MSD should increase by 1.1 mm per day in a normally
developing pregnancy.(37)
Both the quantity and the quality of the fluid are important.
Fluid with echoes, no matter what the quantity, is concerning Crown-rump length (CRL)
for pathology. The differential for anechoic fluid includes Once an embryo is visible, use calipers to measure the CRL.
non-clotted blood, serous fluid, and ascites. Echogenic fluid The yolk is not included in this measurement. While traditional
is assumed to be clotted blood until proven otherwise in the textbooks describe first trimester CRL accuracy to within 5-7
clinical context of suspected hemorrhage but it is important days’ GA, the latest data from in-vitro fertilization labs report
to remember that echogenic fluid may also be due to the even greater accuracy, to within 1 day GA.(38-40) Keep in mind
presence of purulent fluid in the patient with a pelvic infection. though that these calculations are very operator dependent.

37

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2004;191(3):975-978.

40. Diagnostic Ultrasound. In: Rumack C, Wilson S, Charboneau JW,
Levine D, eds. Overview of Obstetric Imaging. Vol One. 4th ed.
Philadelphia: Mosby Elsevier; 2011:1069-1125.

40

CHAPTER 5

APrbengonramnaclyIntrauterine

Creagh Boulger, MD
Melanie Kennedy, MD
Tyler Dschaak, MD

41

SECTION 1

Abnormal Intrauterine Pregnancy

KEY POINTS Pregnancy Failure (Movie 5.1)

1. Serum hCG level should not determine whether or not to Nearly 80% of pregnancy failure occurs in the first trimester.
obtain an ultrasound. (7,8) Approximately 50% of all cases of early pregnancy loss
are due to fetal chromosomal abnormalities.(9) American
2. Use generous threshold levels for diagnosing pregnancy Congress of Obstetricians and Gynecologists (ACOG) defines
failure. early pregnancy loss as a nonviable intrauterine pregnancy
with either an empty gestational sac or a gestational sac
3. First trimester vaginal bleeding has an overall rate of containing an embryo or fetus without fetal heart activity
miscarriage of approximately 10% with higher rates within the first 12 6/7 weeks of gestation.(10) The most
associated with heavy vaginal bleeding and large common risk factors for pregnancy failure are advanced
subchorionic hemorrhage. (1,2) maternal age and prior early pregnancy loss.(11) The risk for
miscarriage, clinically recognized pregnancy loss, increases
4. Sonographic criteria for completed miscarriage: five-fold when maternal age exceeds 40 years compared to
endometrial thickness < 15 mm with no evidence of maternal age between 20-29 years.(12)
retained products of conception. (3-6)
The thresholds for diagnosing pregnancy loss have come
under scrutiny in the past several years. In addition to
the role of Beta-Human Chorionic Gonadotropin (hCG)

42

levels being questioned, sonographic findings for viable and an intrauterine pregnancy was expected on transvaginal (TV)
nonviable pregnancy have been brought into question. The ultrasound.(14-17)
accepted numerical values for crown-rump length (CRL) without
cardiac activity (5mm) and empty gestational sac (GS) (16mm), The hCG level is usually present in the blood within 7 days of
originally thought to be 100 % specific for pregnancy failure, fertilization and continues to rise throughout the first trimester
were found to have wide confidence intervals (Gallery 5.1).(13 ) before declining in the 2nd and 3rd trimesters. It has commonly
Current recommendations advise more generous thresholds in been thought to double every 48 hours during a typical early
diagnosing pregnancy failure in order to avoid placing patients pregnancy; however, many normal pregnancies do not have this
at risk by terminating a desired viable pregnancy.(13) rate of doubling. Only half of all normal singleton pregnancies
will have the hCG level double within 48 hours.(18) When
When approaching the patient with possible pregnancy failure considering a specific threshold for normal hCG level increases,
the emergency physician needs to answer the following Barnhart et al. note that 99 % of viable early pregnancies will
questions: have the hCG level increase at least 24 % when checked at 24
hours, 53 % when checked at 48 hours, and double at one week.
• Where is the pregnancy? (18)
• Is the pregnancy viable?
• Is this definite pregnancy failure, probable failure or unlikely Several studies bring the validity of a single discriminatory
hCG level between 1000-2000 mIU/ml into question.(19-21)
failure? In an eleven year institutional review study, Doubilet et al.
documented nine viable pregnancies with initial hCG levels
In order to answer these questions, the physician should use that exceeded a discriminatory zone of 2000-3000 mIU/L and
the history and physical as well as diagnostic tools such as the initial ultrasound showed no gestational sac.(19) Doubilet
ultrasound and hCG levels. et al. suggest using serial ultrasounds and hCG levels to
guide management in a hemodynamically stable pregnant
Beta-Human Chorionic Gonadotropin patient with a pregnancy of unknown location rather than
HCG is a hormone released by the placenta in pregnant using a single level.(19) Another criticism of using a single
patients. This hormone is what is detected by urine and discriminatory hCG level to differentiate normal from ectopic
serum pregnancy tests. Previous guidelines used a level of pregnancy is the possibility of missing the diagnosis of a
1000-2000 mIU/L international reference preparation (IRP) as multiple gestation pregnancy and misdiagnosing pregnancy
a discriminatory zone above which sonographic evidence of
43

failure or ectopic pregnancy. Multiple gestation pregnancies risk of terminating a viable pregnancy to nearly zero but could
typically have higher hCG levels than singleton gestation potentially delay diagnosis of an ectopic pregnancy and may
pregnancies at the same gestational age.(22) result in unnecessary additional testing for pregnancy failure.

Physicians are responding variably to these new Gestational Sac and Mean Sac Diameter
recommendations. Levine, a radiologist, points out that many A gestational sac (GS) with a 16 mm mean sac diameter (MSD)
radiologists consider these new thresholds overly conservative using TV ultrasound without an obvious embryo was felt to be
which lead to inevitable delays in treatment and unnecessary diagnostic of pregnancy failure; however this threshold only
repeat scans.(23) Creinin, an obstetrician, points out that had a sensitivity of 50 %.(25) Abdallah et al. documented cases
the false positive cases using traditional thresholds are very of viable pregnancies with MSD > 16 mm using TV ultrasound
uncommon (i.e. nine cases in an eleven year review of a busy demonstrating no visible embryo which progressed to viable
institution).(24) ACOG points out that the recommendations pregnancies.(25) A recent study found 19% interobserver
do not include shared decision making between clinician and variability in measuring MSD.(26) By increasing the cutoff
patient.(10) For example, is this patient reliable to comply with for the GS mean sac diameter to 25 mm, the sensitivity and
serial hCG levels and ultrasound? Does the patient desire to specificity approaches 100 % for confirming pregnancy failure.
continue with the pregnancy? Does the patient accept the risks (13)
of delaying an intervention in order to determine with 100 %
accuracy if the pregnancy is viable? Crown-Rump Length (CRL)
Previously a fetal pole with a CRL of 5 mm and no fetal cardiac
Sonographic Findings in Early Pregnancy Failure activity was felt to be diagnostic of pregnancy failure. Meta-
As addressed above, concern for premature termination analysis of published studies demonstrates this cut-off has a
of viable pregnancies has influenced a proposed change sensitivity of 50% and specificity of 100% with 95% confidence
in cut-off levels for viable and nonviable first trimester interval 90-100.(27) Similar to variability in MSD measurements,
pregnancies. In 2013, the Society for Radiologist in Ultrasound Pexsters et al. found 15% interobserver variability in measuring
Multispecialty Panel on Early First Trimester Diagnosis of CRL.(26) When using a cutoff of 5 mm CRL without cardiac
Miscarriage and Exclusion of a Viable Intrauterine Pregnancy activity, the practitioner could diagnosis pregnancy failure
published consensus recommendations (Gallery 5.2).(13) and recommend treatment that could result in termination
Using these more generous thresholds, clinicians lower the of a viable pregnancy. This error in diagnosis can be nearly

44

erased by increasing the CRL cutoff to 7 mm at which point the spotting lasting 1-2 days, the risk of miscarriage during the
specificity approaches 100 %.(13) first trimester is similar to those without bleeding.(1) If heavier
bleeding is present, particularly with painful cramping, up to
The previous criteria for pregnancy failure, CRL of 5 mm 24% of women will miscarry.(1,28)
and MSD of 16 mm without visible embryo, have not been
discarded. However, they are now assigned as measurements Another cause of vaginal bleeding that should be evaluated
suggestive of pregnancy loss rather than diagnostic of is subchorionic hemorrhage. Subchorionic hemorrhage
pregnancy failure. Shared decision making, appropriate is bleeding behind the gestational sac thought to be from
anticipatory guidance and education to patients are critical partial detachment of the chorion.(29) On ultrasound this will
when using these more conservative guidelines. appear as an anechoic or hypoechoic region adjacent to the
GS usually crescentic in shape as it tracks along the perimeter
Miscarriage (Movie 5.2) of the GS. This can be found in approximately 9% of first
trimester pregnancies with vaginal bleeding.(30) Subchorionic
Pregnancy complications are very common in the Emergency hemorrhage is associated with an increased risk of first trimester
Department. Vaginal bleeding in first trimester pregnancies pregnancy loss, estimated at 9% overall risk with an increased
comprise 1.6% of all ED visits in the US.(7) A spontaneous risk up to 19% if the hematoma involves a larger circumference
abortion or miscarriage is a loss of pregnancy prior to 20 weeks’ of chorion elevation.(29,31)
gestation. Miscarriage rates range from 8-22% of patients
who know they are pregnant.(8,10) Understanding the risks of Incomplete Abortion
miscarriage is important when counseling patients who present The hallmark of incomplete abortion is that some but not
with vaginal bleeding in first trimester pregnancies. all products of conception have passed. Diagnosing an
incomplete abortion can be straightforward if a prior ultrasound
Threatened Abortion demonstrated a viable intrauterine pregnancy and follow
Threatened abortion is any bleeding that occurs in a confirmed up ultrasound reveals debris in the uterus or hCG levels are
pregnancy. Approximately 20% of women experience some falling. On ultrasound, incomplete abortions will have varying
bleeding during pregnancy.(2) In women who experience any degrees of endometrial thickness as well as potential definitive
vaginal bleeding in the first trimester, about 10% will miscarry; visualization of placental or fetal tissue.(3) Clinically, the patient
however, the risk of miscarriage varies depending on amount
of bleeding present.(2) For those with only light bleeding or 45

may or may not be bleeding. The mean time to complete a revealed no difference in detection of RPOC and need for
miscarriage with expectant management is 9 days.(32) surgical intervention.(38)

When there is clinical concern for an incomplete miscarriage Molar Pregnancy (Gestational Trophoblastic Disease)
and the ultrasound only demonstrates a thickened (Movie 5.3)
endometrium, color Doppler can be used to identify feeding
vessels associated with retained products of conception (RPOC). In the United States, the incidence of molar pregnancy is 1
Sonographic findings of RPOC typically include the presence of in 1000.(39) The frequency of these pregnancies is higher in
endometrial vascularity and endometrial thickness of 15 mm or Southeast Asia.(39,40) A molar pregnancy is nonviable and
greater.(4,33,34) The absence of Doppler flow on a thickened represents a significant risk to the mother. Pregnancies can
endometrium does not rule out RPOC as they may be avascular. be complete or partial hydatidiform moles, with increased
Clinical suspicion, hCG level, and physical exam findings must rates of malignancy in complete moles.(41) A clinician should
be integrated with the clinician’s sonographic findings when have suspicion for a molar pregnancy when the hCG levels are
evaluating the patient with possible RPOC. significantly higher than expected for the estimated gestational
age. However, in a partial hydatidiform molar pregnancy, the
Complete Abortion hCG levels can be within the normal expected range.(41)
Complete abortion has sonographic, hormonal, and clinical Patients with molar pregnancy often present with exaggerated
findings. On ultrasound, complete abortion will appear as signs of pregnancy, vaginal bleeding, and a nonviable
homogenous intrauterine dimension of less than 15 mm in the pregnancy. In the second trimester, patients may present with
anteroposterior plane on TV ultrasound with no evidence of signs of pre-eclampsia, anemia, and hyperthyroidism.(41)
RPOC.(3,5,6,35) Vaginal bleeding stops and the hCG levels drop.
Following spontaneous abortions, hCG levels decline as follows: On ultrasound, the complete molar pregnancy has a complex,
day 2 levels decline from 21-35% (higher decline with higher intrauterine, echogenic mass that contains many small cystic
starting hCG level); day 7 levels decline 60-84%.(36) In medical structures.(42) This cystic appearance resembles a cluster of
abortions, hCG levels also decline rapidly over the first week grapes. The typical “snowstorm” appearance of complete molar
(mean decline from baseline day one= 57%, day 3= 74%, day 5= pregnancies is usually apparent in the second trimester with
86%, day 6 =93%).(37,38) Following serial hCG levels compared greater variability in appearance in the first trimester.(42) The
with serial ultrasounds to diagnose successful medical abortions partial molar pregnancy is much more difficult to diagnose
on ultrasound, and is often diagnosed by tissue biopsy after

46

pregnancy failure. Sonographic findings often include an 6. Leung SW, Pang MW, Chung TK. Retained products of gestation
abnormally enlarged placenta, enlarged uterus, occasionally a in miscarriage: an evaluation of transvaginal ultrasound
gestational sac and small for gestational age fetus and hydropic criteria for diagnosing an “empty uterus”. Am J Obstet Gynecol.
villi.(43) Given the variability in appearance both complete and 2004;191(4):1133-1137.
partial moles can be confused for RPOC and pregnancy failure.
7. Wittels KA, Pelletier AJ, Brown DF, Camargo CA, Jr. United States
Theca lutein cysts are frequently seen in patients with molar emergency department visits for vaginal bleeding during early
pregnancies.(41,42)  They are thought to originate due to the pregnancy, 1993-2003. Am J Obstet Gynecol. 2008;198(5):523 e521-
excessive amounts of circulating hormone and can also been 526.
seen in other medical conditions associated with elevated
circulating hormone levels.  These cysts are usually seen 8. Wilcox AJ, Weinberg CR, O’Connor JF, et al. Incidence of early loss of
bilaterally and are thin walled with anechoic contents. pregnancy. N Engl J Med. 1988;319(4):189-194.

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15. Brennan DF. Ectopic pregnancy--Part II: Diagnostic procedures and 24. Creinin MD. Further evidence against the reliability of the human
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Gynaecol. 2013;33(2):191-193.

CHAPTER 6

Ectopic Pregnancy

Thompson Kehrl, MD

50