trial

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 medical condition, nor should it be the basis for
the definition of or standard of care that should be practiced by all health care providers at any
particular time or place. Drugs are generally referred to by generic names. In some instances,
brand names might be added for easier recognition.
 
To the fullest extent permitted by law, and without limitation, ACEP expressly disclaims all liability
for errors or omissions contained within this publication, and for damages of any kind or nature,
arising out of use, reference to, reliance on, or performance of such information.
 

Copyright © 2016, American College of Emergency Physicians, Dallas, Texas. All rights reserved.

Except as permitted under the US Copyright Act of 1976, no part of this publication may be
reproduced, stored, or transmitted in any form or by any means, electronic or mechanical,
including storage and retrieval systems, without permission in writing from the publisher. Printed
in the USA.

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.

i

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.

ii

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 pa-
tience 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

iii

Foreword It is hoped that this iBook will assist and encourage providers
to integrate bedside ultrasound into their practices. It is
The Point-of-Care Obstetrical Ultrasound iBook was designed intended to provide direct benefit to patients. The emergency
as a free open access medical education resource for all medicine community has driven the education, research, and
users. Through the leadership of Robert Jones, DO and utilization of point-of-care obstetrical ultrasound. So it is not
Jessica Goldstein, MD, editors, this product represents an surprising that this same group has written what is surely a
innovative educational tool for those who care for pregnant landmark text. Funded through a section grant of the
women. American College of Emergency Physicians, the iBook is one
Obstetric ultrasound is not only a diagnostic tool, but also a in a series of innovative products, tools, and guides that
resuscitative tool.  The emergency physician and point-of care members of the ACEP Emergency Ultrasound Section have
provider can not only evaluate for the presence of pregnancy, created. This product shows the commitment of ACEP and
but also date the pregnancy, determine fetal viability, and Emergency Medicine leaders to bring innovative solutions to
assess the obstetric pelvis. Ultrasound facilitates immediate patients and medical providers. I applaud readers for a
and even lifesaving management decisions. continued commitment to the learning of point-of-care
obstetrical ultrasound.

Resa E. Lewiss, MD, FACEP

ACEP Emergency US Section Chair 2015-2016
Director of Point-of-Care Ultrasound
University of Colorado Hospital
Aurora, CO

iv

Preface

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

Robert A. Jones, DO FACEP
Jessica Goldstein, MD FACEP

v

Contributors

Robert Jones, DO FACEP
Director, Emergency Ultrasound
Director, Emergency Ultrasound Fellowship
Department of Emergency Medicine
MetroHealth Medical Center
Associate Professor, Emergency Medicine
Case Western Reserve University
Cleveland, OH
Co-Editor
Bedside Consult 1st Trimester
Bedside Consult 2nd/3rd Trimester

Jessica Goldstein, MD FACEP
Division Chief, Emergency Medicine
UH Abuja Medical Center
Assistant Professor, Emergency Medicine
Case Western Reserve University
Cleveland, OH
Co-Editor
Normal Intrauterine Pregnancy

Creagh Boulger, MD FACEP
Associate Ultrasound Director
Department of Emergency Medicine
Ohio State University Medical Center
Assistant Professor, Emergency Medicine
Ohio State University
Columbus, OH
Abnormal Intrauterine Pregnancy

Tyler Dschaak, MD
Department of Emergency Medicine
Ohio State University Medical Center
Assistant Professor, Emergency Medicine
Ohio State University

vi

Columbus, OH
Abnormal Intrauterine Pregnancy

Kelly Gibson, MD
Director, Labor and Delivery
Division of Maternal Fetal Medicine
MetroHealth Medical Center
Assistant Professor, Obstetrics and Gynecology
Case Western Reserve University
Cleveland, OH
Second/Third Trimester Pregnancy

Diane Gramer, RDMS, RVT, RT(R)
Ultrasound Educator
Department of Emergency Medicine
MetroHealth Medical Center
Cleveland, OH
Bedside Consult 1st Trimester
Bedside Consult 2nd/3rd Trimester

Thompson Kehrl, MD
Director, Emergency Ultrasound
Director, Emergency Ultrasound Fellowship
Department of Emergency Medicine
Wellspan York Hospital
Clinical Assistant Professor, Emergency Medicine
Drexel University
York, PA
Ectopic Pregnancy

Melanie Kennedy, MD, MSCI
Ultrasound Faculty
Department of Emergency Medicine
Ohio State University Medical Center
Assistant Professor, Emergency Medicine
Ohio State University
Columbus, OH
Abnormal Intrauterine Pregnancy

vii

Justin Lappen, MD FACOG
Fellow, Maternal Fetal Medicine
Department of Obstetrics and Gynecology
MetroHealth Medical Center
Assistant Professor, Reproductive Biology
Case Western Reserve University
Cleveland, OH
Second/Third Trimester Pregnancy

Joseph Minardi, MD FACEP
Director, Emergency Ultrasound
Director, Emergency Ultrasound Fellowship
Department of Emergency Medicine
West Virginia University Medical Center
Associate Professor, Emergency Medicine
West Virginia University,
Morgantown, WV
Incidental Findings

Courtney Smalley, MD
Associate Staff
Emergency Services Institute
Cleveland Clinic
Ultrasound Faculty
MetroHealth Medical Center EMRP
Cleveland, OH
Peer Reviewer

Matthew Tabbut, MD
Associate Director, Emergency Ultrasound
Department of Emergency Medicine
MetroHealth Medical Center
Assistant Professor, Emergency Medicine
Case Western Reserve University
Cleveland, OH
Introduction

viii

CHAPTER 1

1st Trimester
Bedside Consult

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

Scanning Essentials •" Transducer: 5-2 MHz transducer preferred in adult

Clinical Indications patients, but a 5-2 MHz phased array transducer

•" Abdominal or pelvic pain could also be used. A high-frequency linear trans-

•" Vaginal Bleeding ducer can be used to evaluate a gestational sac

•" Maternal trauma for the presence of a yolk sac when not detected

•" Multiple gestations with the curvilinear

•" Fetal viability MOVIE 1.1 Transabdominal Examination transducer.(1)
•" Gestational dating •" Machine setting: Use

the OB/GYN preset.

Focused Questions •" Image optimization:

•" Is there an intrauterine Place desired structure(s) in

pregnancy present the center of the screen and

(MAIN QUESTION)? adjust the gain, time gain

•" Is the embryo or fetus compensation (TGC), and

viable? focal zone(s).

•" How far along is the •" Gel: Use an adequate

embryo or fetus? amount of ultrasound gel on

•" How many embryos or the patient’s lower abdo-

fetuses are present? men.

•" Is there free fluid pre- •" Pelvic scanning proto-

sent? col: Scan the uterus in

BOTH sagittal and trans-

Transabdominal Examina- Transabdominal examination verse planes.
tion Essentials (Movie 1.1) •" Perihepatic window:

•" Patient position: Su- Scan the perihepatic win-

pine. dow if no intrauterine pregnancy found but a signifi-

•" Preparation: A full urinary bladder preferred, but cant amount of pelvic fluid is present.

the examination should be attempted even if the Transabdominal Scanning Protocol ((Gallery 1.1)
urinary bladder is empty.

10

•" Transducer orientation (sagittal): The indicator is •" Image orientation (sagittal): Head is to left of
directed toward the patient’s head (12 o’clock posi- screen, foot is to the right of the screen, anterior is
tion). the top of the image, and posterior is the bottom of
the image.
GALLERY 1.1 Transabdominal First Trimester Ultrasound
•" Transducer location: Start in midline position just
Exam cephalad to pubic bone.

TA sagittal image: Transducer indicator is directed toward •" Identify urinary bladder/uterus.
the patient’s head. The transducer is swept from side-to- •" Slide transducer from side to side as needed since
side so that the entire uterus as well as the anterior and pos-
terior cul-de-sac are visualized. the uterus may be tilted to the left or right.
•" Apply gentle transducer pressure to improve visu-

alization if urinary bladder not full in order to dis-
place 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 sono-
graphic 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 trans-
ducer counterclockwise 90 degrees so indicator is
directed toward the patient’s right (9 o’clock posi-
tion) while centered on uterus in sagittal plane.
•" Transducer orientation (transverse): The indicator
is directed toward the patient’s right (9 o’clock posi-
tion).

11

•" Image orientation (transverse): Anterior is the top ducer. Angling the transducer can be utilized as
of the image, posterior is the bottom of the image, needed.
•" Apply gentle transducer pressure as needed to
GALLERY 1.2 Perihepatic Window improve visualization if urinary bladder not full.
•" Assess cul-de-sacs for free fluid.
Perihepatic window with liver, right kidney and Morison’s •" If no intrauterine pregnancy is seen, then sweep to
pouch visualized. the left and right pelvic sidewalls at the level of the
uterine fundus to evaluate the adnexa.
patient’s right is to the left of the image, and pa-
tient’s left is to the right of the image. Perihepatic Scanning Protocol (Gallery 1.2)
•" Keeping transducer perpendicular to the abdomi- •" Transducer: Use same curvilinear or phased array
nal wall, sweep in both cephalad and caudal direc- transducer.
tions to visualize entire uterus by sliding the trans- •" Transducer location: Place transducer in an inter-
costal oblique position between 8th and 11th ribs in
the mid-axillary line with the indicator directed to-
ward the patient’s axilla.
•" 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 de-
sired 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)

12

•" Patient position: Lithotomy position is preferred. •" Once uterus visualized, gently rotate/angle trans-
Placing blankets or wedges under the patient’s pel- ducer until a true sagittal image of the uterus is
vis on a regular cart is an alternative. identified.

•" Patient preparation: An empty bladder preferred. •" Raise and lower the handle so that the entire
•" A female chaperone should be present and the uterus including the cervix and the cul-de-sacs are

exam explained to the patient. MOVIE 1.2 Transvaginal Scanning
•" Transducer: An endocavitary transducer is used.
•" Machine settings: OB/GYN preset should be used. Transvaginal Scanning
•" Image optimization: Center the target structure(s)
seen (the transducer may need to be pulled out
on the screen and adjust gain, TGC, and focal slightly).
zone(s). •" Anteverted uterus: Raise the handle up to visual-
•" Transducer preparation: Ultrasound gel is first ize lower uterine segment, cervix and posterior-
applied to the transducer footprint followed by plac- cul-de-sac and lower the handle to visualize the
ing the transducer cover and then applying sterile, uterine fundus.
water-soluble gel to the transducer footprint.
13
Transvaginal Sagittal Scanning Protocol (Gallery 1.3)
•" Insert transducer slowly with indicator directed
toward the ceiling (12 o’clock position) until the uri-
nary bladder and uterus are seen.
•" Transducer orientation (sagittal): Indicator is di-
rected toward the ceiling (12 o’clock position).
•" Avoid inserting the transducer all the way into the
vaginal canal since this will potentially limit visuali-
zation.
•" Image orientation (sagittal): Caudal is top of im-
age, cephalad is bottom of image, anterior is to
the left of the image, and posterior is to the right of
the image.

•" Retroverted uterus: Lower the handle to visualize •" If no intrauterine pregnancy seen, then continue to
the lower uterine segment, cervix and cul-de-sac sweep laterally (both left and right) to the pelvic
and raise the handle to visualize the uterine fun- sidewalls in order to visualize the adnexa.

GALLERY 1.3 Transvaginal First Trimester Ultrasound Exam •" With the uterus visualized in a sagittal orientation,
rotate the transducer 90 degrees counterclockwise
to the patient’s right (9 o’clock position).

•" Transducer orientation (coronal): Indicator is di-
rected toward the patient’s right (9 o’clock).

•" Image orientation (coronal): Caudal is top of im-
age, 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.

Place patient in lithotomy position so that transducer han-
dle can be moved up and down.

dus.
•" Sweep the handle to the left and right in order to

visualize the entire uterus in the sagittal plane.

14

•" If no intrauterine pregnancy seen, then angle the •" First sonographic evidence of an intrauterine preg-
handle to the patient’s right to visualize the left nancy.
adnexa (and to the patient’s left to visualize the
right adnexa) at the level of the uterine fundus fol- •" Usually seen by 5-6 weeks’ GA by transvaginal
lowed by raising the handle up and down to sweep exam and one week later by transabdominal
through the adnexa.
GALLERY 1.4 Gestational Sac
Normal Intrauterine Pregnancy
Gestational Sac (Gallery 1.4) Transvaginal transverse image showing an early gestational
sac embedded within the endometrium.
•" Intradecidual sac sign is the first sonographic find-
ing of early pregnancy. exam.
•" Usually seen by a mean sac diameter (MSD)
•" Intrauterine pregnancy confirmation requires pres-
ence of a yolk sac or embryo within the sac. greater than 8 mm.

•" Usually seen by 4.5-5 weeks’ gestational age (GA) 15
by transvaginal exam and one week later by
transabdominal exam.

•" Usually seen by serum hCG of 1000-1500 mIU/ml
(International Reference Preparation [IRP]). This
is referred to as the discriminatory zone.

•" Appears as round or oval, anechoic structure
which is completely embedded within the en-
dometrium eccentrically.

•" The presence of the double decidual sign favors
that the sac is an early gestational sac and not a
pseudogestational sac of an ectopic pregnancy,
but this sign alone should not be used to confirm
the presence of an intrauterine pregnancy.

Yolk Sac (Gallery 1.5)

•" MSD measurement more helpful than serum hCG Embryo (Gallery 1.6)
level in determining the threshold for yolk sac visu- •" Usually seen by 6 weeks’ GA by transvaginal
alization.
GALLERY 1.6 Embryo
GALLERY 1.5 Yolk Sac

Yolk Sac

Yolk Sac Embryo

Transvaginal coronal image showing gestational sac with Transvaginal coronal image with gestational sac containing
internal yolk sac. Note the round shape and anechoic cen- yolk sac and embryo. Crown-rump length (CRL) measure-
ter. ment shown

•" Appears as a round, echogenic ring with a central exam and one week later by transabdominal
anechoic appearance. exam.

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

pregnancy failure.

16

•" Usually seen by a MSD greater than 16 mm. How- GALLERY 1.7 Cul-de-sac Fluid Anterior Cul-
ever, some have suggested increasing the thresh- De-Sac
old for detection to 25 mm or greater. Posterior
Cul-De-Sac
•" MSD measurement more helpful than serum hCG
level in determining the threshold for embryonic Transabdominal sagittal image with large volume of simple
visualization. free fluid in a patient with a ruptured ectopic pregnancy.

•" Appears as an echogenic structure within the amni- suggestive of hemorrhage in the patient with a pos-
otic cavity. sible ectopic pregnancy.
Multiple Gestations (Gallery 1.8)
•" Embryonic cardiac activity should be identifiable •" The chorionicity and amnionicity of a multiple preg-
when the embryo is 5 mm in length or greater. nancy should be determined, if possible
However, some have suggested increasing the •" Dichorionic twins will be diamniotic.
threshold to 7 mm in length or greater to minimize
the chance of falsely diagnosing a pregnancy as 17
nonviable.

•" In embryos with crown-rump length (CRL) less
than 5 mm, the heart rate (HR) should be greater
than 80 beats per minute (BPM).

•" The lower limit of normal for embryonic heart rate
is 100 beats per minute up to 6.2 weeks’ GA and
120 beats per minute at 6.3-7.0 weeks’ GA.

Cul-de-sac Fluid (Gallery 1.7)
•" A small amount of simple fluid (anechoic) may be
seen in normal pregnancies and is termed “physiol-
ogic”.
•" 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

GALLERY 1.8 Multiple Gestations Chorionic Sac •" The twin closest to the cervix should be labeled
twin A and one closest to the fundus should be la-
Amniotic Sac beled twin B.

Monochorionic/monoamniotic twin gestation. Note the •" A subchorionic hemorrhage can be confused with
presence of a single chorionic sac and single amniotic sac. the gestational sac of a twin pregnancy.

•" Amnionicity of monochorionic twins is based on Pregnancy Dating
the number of yolk sacs present. Mean Sac Diameter (MSD)

•" Dichorionic/diamnionic twin gestations occur in •" Performed when gestational sac is visualized but
@25% of cases. embryo is not.

•" Monochorionic/diamnionic twin gestations occur in •" Accurate to within 5-7 days’ GA.
@75% of cases. •" Performed by taking 3 measurements (length,

•" Monochorionic/monoamniotic twin gestations oc- width, and height) of the gestational sac using sag-
cur in @1% of cases. ittal and transverse images of the uterus.

Crown-rump Length (CRL)
•" Performed once the embryo is visualized.
•" Accurate to within 5-7 days’ GA.
•" The yolk sac should not be included in this meas-
urement.
•" Biparietal Diameter (BPD) is more accurate by the
end of the first trimester since fetal flexion and ex-
tension will result in inaccuracies in the CRL meas-
urement.

Pregnancy Failure (Gallery 1.9)
•" Term used to describe early pregnancy nonviabil-
ity.

18

GALLERY 1.9 Pregnancy Failure teria uses embryo greater than 7 mm in length
without cardiac activity).
•" Possible findings include: abnormal gestational
sacs features, a MSD greater than 8 mm with no
yolk sac visualized, or a MSD greater than 16 mm
with no embryo visualized (Proposed criteria uses
MSD greater than 25 mm with no embryo visual-
ized).
•" In cases of possible pregnancy failure, it is always
best to give the pregnancy the benefit of the doubt

GALLERY 1.10 Gestational Trophoblastic Disease

Transabdominal sagittal image with definitive pregnancy
failure. Embryo has crown-rump length greater than 7 mm
in length with absence of cardiac activity.

•" Other terms, such as anembryonic pregnancy, Transvaginal coronal image with endometrium containing
intrauterine fetal demise, and blighted ovum can multiple small cystic spaces surrounded by echogenic tis-
be confusing and should be avoided. sue.

•" Current controversy surrounding the sonographic 19
discriminatory zones.

•" Definitive evidence based on current criteria in-
cludes the presence of an embryo greater than 5
mm in length without cardiac activity (Proposed cri-

and recommend a follow up ultrasound and repeat ened endometrium with echogenic material pre-

serum hCG level. sent, but this is a non-specific finding.

•" Definitive findings include the presence of placen-

Gestational Trophoblastic Disease (Gallery 1.10) tal or fetal tissue.

•" A complete mole will •" Color Doppler can be

appear as a large, com- GALLERY 1.11 Ectopic Pregnancy used to identify feeding ves-
plex mass within the en- sels associated with RPOC.

dometrial cavity with •" The diagnosis of a com-

multiple small cystic pleted miscarriage cannot

spaces surrounded by be made with certainty just

echogenic tissue (the by the ultrasound findings

“cluster of grapes” ap- alone (need to correlate with

pearance). history and physical exam

•" Classic sonographic findings). If a prior ultra-

findings are more com- sound confirming an IUP or

mon in the second tri- definitive evidence of pas-

mester. sage of an IUP are not avail-

•" A partial mole is a form able, one should be careful

of disease in which both in interpreting the findings of

a fetus and abnormal a normal ultrasound.

trophoblastic tissue are

present. Commonly, Illustration showing ectopic pregnancy locations.

the fetus has an abnor- Ectopic Pregnancy (Gal-

mal sonographic appear- lery 1.11)

ance. Anatomic Locations

•"Fallopian tube- @95%

Partial vs. Complete Mis- •"Interstitial- @2-4%

carriage •" Ovary- @0.5%

•" The sonographic findings associated with retained •" Cervix- @0.1%

products of conception (RPOC) include a thick- •" Abdominal- @0.03%

20

Endometrial Findings nonviable embryo suggests the cervical phase of
•" Trilaminar appearance is specific but not sensitive a spontaneous miscarriage.
for the diagnosis of ectopic pregnancy. •" Serial scans are recommended if the diagnosis
•" Pseudogestational sacs are seen in @10 percent remains in doubt after ultrasound examination.
of ectopic pregnancies.
Abdominal Ectopic
Tubal Ectopic •" Ultrasound will demonstrate a fetus within the peri-
•" Definitive sonographic findings include the identifi- toneal cavity.
cation of a gestational sac containing an embryo •" These are exceeding rare.
or yolk sac. •" Most commonly found in the posterior cul-de-sac
•" Nonspecific findings include adnexal (tubal) ring, or adjacent to the fundus of the uterus.
complex mass and free fluid.
Heterotopic Pregnancy
Interstitial Ectopic •" Heterotopic pregnancies are more common in
•" Sonographic findings include an empty uterine patients who have undergone assisted reproduc-
cavity with a chorionic sac < 5 mm from the tion than in the general population.
myometrial border. •" In patients who have undergone assisted reproduc-
•" Uterine contractions resulting in an eccentrically tion, expect unusual combinations including multi-
located but normally implanted uterine sac, an ple IUPs and multiple extrauterine pregnancies.
early IUP in a bicornuate uterus, and a uterine fi- •" In a patient who has undergone assisted reproduc-
broid in a pregnant patient without a visualized tion, the adnexal, cervical, and cornual regions
IUP can all be mistaken for an interstitial ectopic must be scanned even if an intrauterine preg-
pregnancy. nancy is found.

Cervical Ectopic References:
•" Sonographically, implantation will be visualized in
the cervical region. 1. Tabbut M, Harper D, Gramer D, Jones R. High-frequency
•" The presence of cardiac activity strongly suggests linear transducer improves detection of an intrauterine
a cervical ectopic, while an abnormal sac with a pregnancy in first-trimester ultrasonography. Am J Emerg
Med. 2016;34(2):288-291.

21

CHAPTER 2

2nd/3rd Trimester
Bedside Consult

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

Scanning Essentials •" Machine setting: Use the OB/GYN preset.
Clinical Indications •" Gel: Use an adequate amount of ultrasound gel.
•" Image optimization: Place desired structure(s) in
•" Abdominal or pelvic pain
•" Vaginal bleeding center of screen and adjust gain, TGC, and focal
•" Maternal trauma zone(s).
•" Maternal critical illness •" Pelvic scanning protocol: The uterus is scanned in
•" Fetal number BOTH sagittal and transverse planes.
•" Fetal viability •" eFAST scanning protocol: Performed in cases of
•" Fetal presentation maternal trauma.
•" Gestational dating
•" Placental localization Transabdominal Scanning Protocol
•" Fetal lie and presentation
Focused Questions •" Fetal cardiac activity
•" How many fetuses are present? •" Fetal number
•" Is the fetus viable? •" Amniotic fluid volume
•" How far along is the fetus? •" Placental localization
•" Where is the placenta located? • Fetal biometry
•" What is the fetal presentation/lie?
•" Is there sonographic evidence of Sonographic Findings
hemoperitoneum/hemopericardium/pneumothorax
(maternal trauma)? Fetal Lie and Presentation (Gallery 2.1)
•" Fetal lie and orientation of the fetal spine relative
Transabdominal Examination Essentials to the maternal spine.
•" Patient position: Supine (with wedge under pa- •" Determination requires obtaining a mid-sagittal
tient’s right side to displace the uterus off of the in- view of the fetal spine.
ferior vena cava). •" Fetal lie: longitudinal (fetal and maternal spines
•" Preparation: None. parallel), transverse (fetal spine is perpendicular to
•" Transducer: 5-2 MHz curvilinear probe preferred in the maternal spine), and oblique (angle between
adult patients, but a phased array probe of similar longitudinal and horizontal).
frequency could also be used.
23

•" Fetal presentation refers to which anatomic part of •" Presence or absence has significant management
the fetus is closest to the pelvic inlet (cephalic, implications.
breech, or shoulder).
•" Can be calculated using M-mode or pulsed-wave
GALLERY 2.1 Fetal Lie and Presentation Doppler (M-mode preferred).

Longitudinal Fetal Lie Fetal Number (Gallery 2.2)
•" Multiple gestations associated with numerous preg-
Cephalic Breech nancy complications.

GALLERY 2.2 Fetal Number

Amniotic Sac Chorionic Sac

Maternal and fetal spines are parallel

Longitudinal fetal lie.

•" Fetus in cephalic or breech presentation has a Monochorionic, monoamniotic twin pregnancy
longitudinal lie.
24
Fetal Cardiac Activity

•" Determination of fetal number requires scanning •" Oligohydramnios and polyhydramnios are both
the entire uterine cavity in a systematic fashion associated with and increased risk of perinatal
with attention to the number of fetal crania. morbidity and mortality.

•" Look for a dividing membrane which indicates a •" Maximal vertical pocket (MVP) and amniotic fluid
diamniotic pregnancy (Di-Di or Mono-Di). index (AFI) are the two methods for assessing am-
niotic fluid volume (MVP is the preferred method
Amniotic Fluid Volume (Gallery 2.3) due to simplicity and lower false positive rate for
•" Primary source of amniotic fluid in the 2nd/3rd tri- oligohydramnios).
mester is fetal urine.
GALLERY 2.3 Amniotic Fluid Volume •" Normal MVP ranges from 2-8 cm.
•" Oligohydramnios is defined as MVP < 2 cm.
Maximum vertical pocket (single largest pocket free of um- •" Polyhydramnios is defined as MVP > 8 cm.
bilical cord or fetal parts). Normal is between 2-8 cm.
Placental Localization/Assessment (Gallery 2.4)
•" Identification of placenta previa essential since
these patients require C-section.
•" Low-lying placenta previa: edge within 2 cm of
cervical os but does not touch the internal cervical
os.
•" Marginal placenta previa: edge touches the inter-
nal cervical os but does not cover it.
•" Complete placenta previa: placenta covers the
internal cervical os.
•" A full urinary bladder or focal myometrial contrac-
tions may make the placenta appear closer to the
internal cervical os than it really is so rescan the
patient with bladder empty or after contraction
ends if placenta previa is questioned.
•" Transvaginal ultrasound should be used to confirm
questionable placenta previa seen on transabdomi-
nal ultrasound.

25

•" Vasa previa refers to the presence of fetal blood GALLERY 2.5 Fetal Biometry
vessels between the presenting fetal parts and the
cervix and is associated with significant perinatal Biparietal Diameter (BPD)
mortality.
• Transverse section at level of
GALLERY 2.4 Placental Localization/Assessment thalami (t) and cavum septae
pellucidum (csp)
Low-Lying Placenta Previa
• Cerebellar hemispheres NOT
visualized

• Outer wall-to-inner wall of the
parietal bones

Image courtesy EMSONO Biparietal diameter. Measurement is an outer wall-to-
inner wall measurement of the parietal bones at the level of
Low-lying placenta. the thalami (t) and cavum septae pellucidum (csp).

•" Abruptio placenta: sonographic findings include in the detection of abruptio placenta is low and
the presence of a retroplacental clot but it is essen- therefore cannot exclude the diagnosis.
tial to understand that the sensitivity of ultrasound
Fetal Biometry (Gallery 2.5)
•" Head circumference and biparietal diameter: meas-
ured in a transverse section of the head at the
level of the thalami and cavum septi pellucidi.

26

•" Abdominal circumference: symmetrical, circular
transverse section of the fetal abdomen that in-
cludes visualization of the vertebrae in cross sec-
tion, the stomach bubble, and intrahepatic umbili-
cal vein with portal sinus.

•" Femur length: measured in full length of the bone
perpendicular to the ultrasound beam EXCLUD-
ING 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).

27

CHAPTER 3

Introduction

Matthew Tabbut, MD

SECTION 1
Introduction

KEY POINTS Role of ultrasound in pregnancy

1. Ultrasound plays an integral role in the It is estimated that over 211 million pregnancies occur every
evaluation of the pregnant patient. year worldwide with pregnancy complications being the
leading cause of mortality among women of childbearing
2. Point-of-care ultrasound enhances the years.(1) In 2015 over 300,000 women died of pregnancy
bedside evaluation of the pregnant patient. related complications with a maternal mortality rate worldwide
equaling approximately 200 maternal deaths per 100,000 live
3. Point-of-care ultrasound examinations are births. Countries of impoverished economic means are
focused studies designed to answer disparately affected, most notably Sub-Saharan Africa. In
specific clinical questions. developed countries, mortality has fallen over the last half
century to approximately 12 maternal deaths per 100,000 live
4. Point-of-care ultrasound is not meant to births.(2) This decrease is believed to be in part due to the
replace comprehensive ultrasound use of ultrasound in prenatal care.(3, 4) The World Health
imaging. 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 mortality are
similar.(5) Ultrasound has revolutionized the medical care

29

provided during pregnancy both as a screening tool for now being performed and interpreted by the clinical physician
pregnancy and fetal complications in the evaluation of the at the “point-of-care”, thus allowing for a seamless integration
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) to
performed at planned intervals for the purpose of fetal 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
trimester, ultrasound is used to assess fetal and placental imaging in its scope. Whereas traditional imaging is
development. In the third trimester, ultrasound is used to performed and evaluated by imaging specialists who are
further monitor fetal development, for delivery planning and trained to perform studies and analyze images in a
screening for potential complications of delivery. However comprehensive manner; POCUS is by definition a limited
when the pregnant patient is acutely injured or ill, rapid study, focused on an organ system or specific area of concern
assessment includes ultrasound to assess for fetal location, which seeks to answer focused questions pertinent to patient
viability and pregnancy related complications as well as non- care. Clinicians throughout the house of medicine use
pregnancy related pathology. POCUS at the bedside to assist with their clinical exam and
diagnostic assessment.(6)
Ultrasound at the bedside
When evaluating the acutely ill or injured pregnant patient,
Traditionally ultrasound has been performed in a often the clinical exam is of limited utility and fetal imaging is
comprehensive manner in specific imaging suites. Similar to necessary. POCUS is extremely valuable in answering
other modalities, ultrasound imaging is typically performed specific questions related to the patient condition (i.e. Is there
and interpreted by physicians specializing in imaging who an intra-uterine or ectopic pregnancy? What is the fetal heart
may not be directly involved in clinically assessing or caring rate? What is the gestational age? Is there free fluid?
for the patient. However as developing technology has Where is the placenta? Is the fetus vertex or breach?)
allowed for smaller and more portable ultrasound machines, Ultrasound has been shown to be useful in the hands of
the use of ultrasound has been brought to the bedside and is clinical physicians to rapidly identify normal pregnancy,
diagnose obstetric emergencies, and guide management

30

especially in the first trimester.(7-11) Additionally it has been acute findings. Since the goal of POCUS is to answer
shown to provide results more rapidly than consultative specific and pertinent clinical questions, pregnant women
ultrasound.(12, 13) As such, the use of point-of-care must still undergo traditional, comprehensive prenatal
ultrasound has become an integral part of the evaluation of ultrasound surveillance. Additionally, since POCUS can yield
the pregnant patient presenting with variety of acute uncertain, indeterminate or unexpected findings, these
complaints. patients often require referral for comprehensive fetal
diagnostic imaging.
Point-of-care ultrasound in the pregnant patient is not
intended to obviate the need for comprehensive sonography. In summary, modern obstetrical care relies heavily on
Understanding the limitations of POCUS is important for the ultrasound in the routine evaluation of the uncomplicated
physician using ultrasound in the bedside evaluation of pregnancy and the management of the acutely ill or injured
patients. pregnant patient. While there remains a role for
comprehensive imaging, POCUS enhances the evaluation
Despite the benefits to performing and interpreting ultrasound and management of pregnant patients by interpreting
imaging at the bedside, ultrasound acquisition and ultrasound findings within the clinical context at the bedside to
interpretation is more operator dependent than other imaging answer pertinent clinical questions.
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
While POCUS is useful in answering pertinent clinical Organization Press; 2005.
questions, the list of differential diagnoses of concern to the
physician caring for the acutely ill or injured pregnant patient 2 Alkema L, Chou D, Hogan D, et al. Global, regional, and
does not reflect the entirety of pathologies that can adversely national levels and trends in maternal mortality between 1990
affect pregnant women or fetuses (i.e. malignancies, adnexal and 2015, with scenario-based projections to 2030: a
pathology, congenital fetal anomalies, etc.). Traditional systematic analysis by the UN Maternal Mortality Estimation
imaging specialists such as radiology or obstetrics perform Inter-Agency Group. Lancet. 2016 Jan 30;387(10017):462-74.
comprehensive imaging studies that look for features of an
expanded differential diagnosis consisting of acute and non- 31

3 Harris RD, Marks WM. Compact ultrasound for improving 9 Stein JC, Wang R, Adler N, et al. Emergency physician
maternal and perinatal care in low-resource settings: review ultrasonography for evaluating patients at risk for ectopic
of the potential benefits, implementation challenges, and pregnancy: a meta-analysis. Ann Emerg Med. 2010 Dec;
public health issues. J Ultrasound Med. 2009 Aug;28(8): 56(6):674-83.
1067-76. 10 Adhikari S, Blaivas M, Lyon M. Diagnosis and
management of ectopic pregnancy using bedside transvaginal
4 Akinmoladun JA, Ogbole GI, Lawal TA, Adesina OA. ultrasonography in the ED: a 2-year experience. Am J Emerg
Routine prenatal ultrasound anomaly screening program in a Med. 2007 Jul;25(6):591-6.
Nigerian university hospital: Redefining obstetrics practice in 11 Bailey C, Carnell J, Vahidnia F, et al. Accuracy of
a developing African country. Niger Med J. 2015 Jul-Aug; emergency physicians using ultrasound measurement of
56(4):263-7. crown-rump length to estimate gestational age in pregnant
females. Am J Emerg Med. 2012 Oct;30(8):1627-9.
5 Creanga AA, Berg CJ, Syverson C, Seed K, Bruce FC, 12 Blaivas M, Sierzenski P, Plecque D, Lambert M. Do
Callaghan WM. Pregnancy-related mortality in the United emergency physicians save time when locating a live
States, 2006-2010. Obstet Gynecol. 2015 Jan;125(1):5-12. intrauterine pregnancy with bedside ultrasonography? Acad
Emerg Med. 2000 Sep;7(9):988-93.
6 Moore C, Todd WM, O'Brien E, Lin H. Free fluid in Morison's 13 Shih CH. Effect of emergency physician-performed pelvic
pouch on bedside ultrasound predicts need for operative sonography on length of stay in the emergency department.
intervention in suspected ectopic pregnancy. Acad Emerg Ann Emerg Med. 1997 Mar;29(3):348-51; discussion 52.
Med. 2007 Aug;14(8):755-8.
32
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.

CHAPTER 4

Normal Intrauterine
Pregnancy

Jessica Goldstein, MD

SECTION 1
Normal Intrauterine Pregnancy

KEY POINTS Embryosonology
Gestational Dating Terminology
1. Gestational age starts with the first day of The first trimester of pregnancy spans thirteen weeks from the
the last menstrual period (FDLMP). first day of a woman’s last menstrual period (FDLMP).
Conception occurs approximately two weeks following the
2. The yolk sac is the first reliable sign of an FDLMP. Clinicians use gestational age (GA) to measure the
intrauterine pregnancy (IUP). developmental age of the embryo and fetus, while
embryologists use fertilization age to measure the
3. Crown-rump length is accurate to within developmental age of the embryo and fetus. GA begins with
5-7 days gestational age (GA). the FDLMP. All dates presented in this iBook will be in GA.

4. The presence of a gestational sac does Embryologic Periods of the First Trimester (Gallery 4.1)
not definitively diagnose the presence of 1." Ovarian period—the first 1-2 weeks’ GA
an intrauterine pregnancy (IUP). 2." Conceptus period—the 3-5 weeks’ GA
3." Embryonic period—the 6-10 weeks’ GA

34

4." Fetal period—the 11-12 weeks’ GA for implantation at approximately 20-21 days’ GA.(1) The

implantation process is completed by approximately 23 days’

GA and embryogenesis continues.(1) However, it is not until

Ovulation 4.5 to 5 weeks’ GA that the first reliable sonographic evidence
Ovulation occurs at of an intrauterine pregnancy (IUP) is visualized.

approximately 14 days after GALLERY 4.1 Ovulation Through Implantation
the FDLMP. It is during
ovulation that the maturing Gestational Sac (Movie 4.1)

follicle releases the egg Clinical Pearls:

(oocyte) along with follicular 1." A gestational sac (GS) is the
fluid into the peritoneal first visible sonographic sign of an
cavity. The oocyte enters intrauterine pregnancy (IUP).
the fallopian tube and makes

its way towards the waiting 2." IUP confirmation requires the
sperm. If the oocyte is not presence of a yolk sac or embryo
fertilized, the corpus luteum within the sac.
involutes.
3." A GS is a round or ovoid

structure embedded in the decidua

Fertilization/Implantation in the mid to upper 1/3 of the
uterine fundus.
Fertilization occurs when the Illustration depicting ovulation through implantation.
sperm and oocyte unite to 4." A pseudogestational sac of an
form the zygote in the outer ectopic pregnancy may be
third of the fallopian tube (Figure). The zygote undergoes confused for an early GS.

cellular division as it travels through the fallopian tube and by 5." The discriminatory zone for detection of a GS is
approximately 17 days’ GA reaches the uterus.(1) The zygote approximately 1000 -1500 mIU/ml (International Reference
has matured into the blastocyst stage by the time it is ready Preparation [IRP]) via transvaginal (TV) ultrasound; however

35

an hCG level below the threshold should not dissuade the were absent in at least 35% of GS when current TV
clinician from ordering an ultrasound if an abnormal sonographic technology was used and that interobserver
variability in interpreting these signs was high.(4)
MOVIE 4.1 Gestational Sac
The intradecidual sac sign consists of a circular, anechoic
Gestational Sac structure measuring only a few millimeters which is
pregnancy is suspected. completely embedded within the endometrium, abuts the
Two sonographic signs of early pregnancy, the intradecidual endometrial stripe, and does not deform the midline
sign and the double decidual sign, were defined in the 1980s, endometrial stripe. It is usually seen by 4.5 weeks’ GA by TV
prior to the widespread use of TV ultrasound.(2,3) These ultrasound.(2) This finding is unfortunately neither sensitive
signs were first described as a method of differentiation nor specific enough to definitively diagnose the presence of
between an early IUP and the pseudogestational sac of an an IUP.
ectopic pregnancy. A recent study found that these signs
The double decidual sac sign is seen as two echogenic rings
surrounding the anechoic gestational sac (Gallery 4.2). The
outer ring is formed by decidua parietalis (also called vera)
and the inner ring is formed by decidua capsularis. It is
usually seen 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 the widespread availability of transvaginal
ultrasound when the interval between GS and YS
visualization on TA scanning was longer. This finding is also
neither sensitive nor specific enough to definitively diagnose
the presence of an IUP and should be interpreted with
caution.

36

The differential for an intrauterine sac includes 1) a sensitivity and varying reported specificity for ectopic
pseudogestational sac of an ectopic pregnancy and 2) a pregnant.(6,9) Benson et al. reported that fluid can be seen
decidual cyst. Pseudogestational sacs, once reported as in the uterus in 16.6% of patients with ectopic pregnancy but
occurring in 20% of ectopic pregnancies, have more recently concluded that in the vast majority of cases, it can be
distinguished from an early intrauterine gestational sac based
GALLERY 4.2 Decidual Layers
MOVIE 4.2 Yolk Sac

Illustration depicting decidual layers of the intrauterine Yolk Sac
pregnancy.
on shape, contents, and/or location.(10) Decidual cysts
been estimated in 5-10% of ectopic pregnancies.(5-8) A represent areas of decidual breakdown and tend to be located
pseudogestational sac is thought to result from away from the endometrial stripe while early gestational sacs
decidualization of the endometrium from hormones produced will abut against the endometrial stripe.
by an ectopic pregnancy. Pseudogestational sacs have low
37

Yolk Sac (Movie 4.2) pregnancy failure.(4) The upper limit of the yolk sac diameter
Clinical Pearls: between 5-10 weeks GA is about 5-6 mm and it has been
generally accepted that an abnormally large yolk sac
1." The yolk sac is the first reliable sign of an IUP. indicates a poor obstetrical outcome.(13,15,16) The absence
of a yolk sac in the presence of an embryo is always
2." The yolk sac is usually seen by 5.5 weeks’ GA by TV abnormal. The controversy surrounding the threshold values
ultrasound. for detection of yolk sac will be discussed in greater detail in
the Pregnancy Failure and Ectopic Pregnancy sections of this
3." Sonographically appears as a round, echogenic ring with iBook.
a central anechoic appearance.
Fetal Pole/Embryo (Movie 4.3)
4." The yolk sac is usually seen with TV ultrasound when
the mean sac diameter (MSD) is 8 mm. Clinical Pearls:

The first reliable sign of an IUP is the yolk sac which is visible 1." With TV scanning, the embryo is visible by 6 weeks’ GA.
by about 5.5 weeks’ GA with TV ultrasound.(11) The yolk sac
provides nutrition to the growing embryo until the placental 2." Cardiac activity should be visible when the embryo is 5
circulation takes over. As the umbilical cord and placenta mm in length (crown-rump length).
grow, the yolk sac becomes obsolete and is no longer visible
at about 12 weeks’ GA.(12) Initially, the yolk sac appears as 3." At 10 weeks’ GA, the embryo is called a fetus.
a round, echogenic ring located eccentrically within the
gestational sac. The clinical significance of an irregular yolk The fetal pole is the developing embryo. It first appears as an
sac shape with wrinkled margins or indented walls is not echogenic speck on the yolk sac which resembles a diamond
known and is controversial.(13) The threshold for ring. The embryo starts to fold and pinches off the roof of the
sonographic visualization of the yolk sac is best made from yolk sac to form the embryonic mid-gut. A portion of the
the mean sac diameter (MSD) measurement and not the hCG posterior yolk sac differentiates into the allantois which
level. The yolk sac should be visible when the MSD of the GS eventually becomes the umbilical cord. At about 6 weeks’
is 8 mm by TV ultrasound; however, the yolk sac may appear GA, the embryo and yolk sac are suspended within the
later as the MSD approaches 20 mm so one needs to be gestational sac by the allantois. At this point, the embryo
cautious when interpreting these numbers.(4,14) Absence of appears as a grain of rice and is normally visible with
a yolk sac when the MSD is 16-24 mm is highly suspicious for
38

transvaginal ultrasound when its length is 2-4 mm. After 10 120-160 BPM with varying means reported, independent of
weeks’ GA, the embryo is called a fetus. gender.(19,20)

Fetal Heart Rate (FHR) Cardiac activity should be visible when the CRL is 5 mm by
TV ultrasound, although some have suggested increasing the
Embryonic cardiac activity is usually seen by approximately 6
threshold criteria to 7 mm by TV
weeks’ GA with TV MOVIE 4.3 Embryo ultrasound in order to minimize the
ultrasound. In an in-vitro false-positive diagnosis of
pregnancy failure.(14,21) The
fertilization lab population, FHR is measured using M-mode.
While Doppler can be used to
which differs from an measure embryonic or fetal cardiac
activity during the first trimester, M-
Emergency Department mode focuses lower energy than
Doppler on the developing embryo
patient population, fetal and therefore M-mode is the
preferred measurement tool.
cardiac activity at 6 weeks’
Amnion
GA has a 93% positive Clinical Pearls:

predictive value of 1." The amnion expands around
the developing embryo.
completing the first trimester.
2." The amnion is visible when the CRL is 2 mm.
(17) With improved
3." The amnion fuses with the chorionic cavity at 14-16
ultrasound technology, weeks’ GA.

embryonic cardiac activity 39

can be seen as early as a

crown-rump length (CRL) of

2 mm. When embryonic

cardiac activity is first Embryo
visualized, the heart rate is

usually around 100-120

beats per minute (BPM). 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 6.3-7.0 weeks’ GA.(18) The FHR

plateaus after 9 weeks’ GA and the normal FHR ranges from

The amnion derives from the inner cell mass and expands Multiple Gestations (Movie 4.4)
around the embryo as it develops. Though the amnion Clinical Pearls:
develops prior to the yolk sac, it is not visualized by
ultrasound until after the yolk sac develops and the embryo 1." Dizygotic (fraternal) twins always have separate chorion,
starts to enlarge. The amnion is visible when the CRL is yolk sacs, amnion and placenta.

MOVIE 4.4 Multiple Gestations 2." Monozygotic (identical) twins may have separate
chorionic sacs (dichorionic) or they may share a chorionic sac
Multiple Gestations (monochorionic) depending on when embryonic separation
about 2 mm.(2) The amnion grows like a balloon around the occurs.
developing embryo and provides a fluid buffer between the
fetus and the uterus. The amnion is always separate from the 3." Dichorionicity confers the greatest survival for twin
yolk sac. At approximately 14-16 weeks’ GA, the amniotic pregnancies.
cavity fuses with the chorionic cavity.
4." The chorionicity and amnionicity of a multiple pregnancy
should be documented as early as possible.

5." In monochorionic twins, amnionicity is based on the
number of yolk sacs present.

The rate of twin pregnancies in the US has climbed since the
1980s due to increased maternal age and assisted
reproductive technology. The latest statistics from the
National Vital Statistics Report of 2013 report the incidence of
twin pregnancies of 33.9/1000 live births and triplet and
higher pregnancies 113.5/100,000 live births.(22) The
frequency of spontaneous monozygotic (MZ) twins remains
constant across populations at approximately 3/1000 live
births whereas the rates of spontaneous dizygotic (DZ) twins

40

varies by numerous factors including geography, maternal which is a projection of placental tissue extending between
age, and socioeconomic factors.(23-30) the two adjacent chorionic sacs. Partial fusion of the placenta
and chorion is common in dichorionic pregnancies and does
Dichorionic not lead to twin-to-twin transfusion.

Abbreviations used to describe the type of twin pregnancy Monochorionic
refer to the chorionicity (monochorionic versus dichorionic)
and the amnionicity (monoamniotic versus diamniotic). The most common type of identical twin pregnancy, occurring
Chorionicity determines the likelihood of twin fetal survival in about 70-75% of spontaneous monozygotic twins, is
with dichorionic pregnancy conferring the best outcomes. monochorionic, diamniotic (Mono-Di).(31) This twin
pregnancy occurs when the inner cell mass splits between
Dizygotic 4-8 days after conception. In monochorionic twins,
amnionicity is based on the number of yolk sacs present. If
Dizygotic twins are always dichorionic, diamniotic (Di-Di). there are two yolk sacs seen, the pregnancy is Mono-Di. The
embryos will have one chorion and placenta, but separate
Monozygotic yolk sacs and amnions. On ultrasound, look for one
gestational sac and 2 yolk sacs. If the amniotic sacs can be
Chorionicity of monozygotic twins depends on the timing of seen, they will have a thin dividing membrane. Twin- to-twin
separation of the fertilized egg. Monozygotic dichorionic, transfusion is a risk that occurs in 10-15% of Mono-Di
diamniotic (Di-Di) twins occur when the inner cell mass of the pregnancies when two embryos share one placenta and more
blastocyst splits into two completely separate blastocysts less blood flow is directed to one of the embryos.(32)
than 4-days post conception. When the blastocysts implant at
completely different sites, they have separate chorion, yolk Much less common in monozygotic twins and in conjoined
sacs, amnion and placenta. If the blastocysts implant closely, twins, the inner cell mass separates late (> 8 days post
the chorions may fuse, but the vascular supply to each conception) or incompletely and the embryos share a chorion,
embryo remains separate. About 25-30% of spontaneous yolk sac, amnion, and placenta (monochorionic,
identical twins are Di-Di.(31) monoamniotic or Mono-Mono). Mono-Mono pregnancies are
described in rare case reports and are frequently complicated
In first trimester scans, look for two thick walled chorionic by umbilical cord entanglement.(33,34) Conjoined twins are
sacs and two separate yolk sacs. Do not confuse the even rarer.
rhombencephalon of the developing fetal brain for a second
yolk sac. At 11-14 weeks’ GA, look for the twin peak sign, 41

"Vanishing twin" occurs when an embryo that was identified pregnancies scanned prior to 20 weeks.(36) The first
on an early pregnancy ultrasound disappears on a later trimester is the best time to determine chorionicity so the
ultrasound. Vanishing twin occurs more frequently in point-of-care user should include this information on reports
monochorionic pregnancies than dichorionic (8.3% vs 2.6%). when possible.
(35)
Free fluid (Movie 4.5)
MOVIE 4.5 Free Fluid Clinical Pearls:

Free Fluid 1." Physiologic free fluid is small in volume and echo-free.
It is important to document the number of chorionic sacs, yolk
sacs, and embryos as early as possible so that the risks of 2." Echogenic fluid should be assumed to be blood until
fetal morbidity are known and can be monitored closely. In a proven otherwise in the clinical context of suspected
2014 twin study with highly trained sonographers, the hemorrhage.
chorionicity of the twins was misdiagnosed in 6.4% of
3." Ultrasound cannot differentiate between purulent debris
and hemorrhage when echogenic fluid is present.

Physiologic fluid is often seen in pregnant and non-pregnant
females. Fluid visualized in the lower uterine segment of the
posterior cul-de-sac is considered a small volume. A
moderate volume of fluid extends beyond the lower uterine
segment. A large volume of fluid would potentially surround
the uterus extending into the anterior cul-de-sac and possibly
to Morison’s pouch in the right upper quadrant.

Both the quantity and the quality of the fluid are important.
Fluid with echoes, no matter what the quantity, is concerning
for pathology. The differential for anechoic fluid includes non-
clotted blood, serous fluid, and ascites. Echogenic fluid is
assumed to be clotted blood until proven otherwise in the

42

clinical context of suspected hemorrhage but it is important to when the MSD is 8 mm or greater and an embryo when the
remember that echogenic fluid may also be due to the MSD is 16 mm or greater. Patients must be followed closely
presence of purulent fluid in the patient with a pelvic infection. with serial hCG levels and ultrasound when expected
embryologic developments are not seen. MSD should
4G.e6s)tational Dating (Movie MOVIE 4.6 Gestational Dating increase by 1.1 mm per day in a normally developing
Clinical Pearls:
pregnancy.(37)
1." First trimester dating is Crown-rump length (CRL)
the most reliable period for Once an embryo is visible, use
estimating GA. calipers to measure the CRL. The
yolk is not included in this
2." CRL is accurate to measurement. While traditional
within 5-7 days’ GA. textbooks describe first trimester
CRL accuracy to within 5-7 days’
3." Use m-mode to GA, the latest data from in-vitro
calculate FHR. fertilization labs report even greater
accuracy, to within 1 day GA.
4." When the CRL is 5 mm, (38-40) Keep in mind though that
FHR should be > 100 BPM. these calculations are very
operator dependent.
Mean Sac Diameter (MSD)
43
of the gestational sac is Gestational Dating
accurate to within 5-7 days’

GA. Depending on the

machine, the measurement will be the average of three

orthogonally oriented diameters in the AP and sagittal planes

or just one diameter with the assumption the sac is round. A

standardized calculation package will estimate the age based

on the MSD. A yolk sac will usually be seen with TV scanning

References: 8." Hill LM, Kislak S, Martin JG. Transvaginal sonographic
detection of the pseudogestational sac associated with
1." The Developing Human: Clinically Oriented Embryology. ectopic pregnancy. Obstet Gynecol. 1990;75(6):986-988.
In: Moore K, Persaud TVN, Torchia M, eds. 10th ed.
Philadelphia: Elsevier; 2016:33-35. 9." Ahmed AA, Tom BD, Calabrese P. Ectopic pregnancy
diagnosis and the pseudo-sac. Fertil Steril. 2004;81(5):
2." Yeh HC. Sonographic signs of early pregnancy. Crit Rev 1225-1228.
Diagn Imaging. 1988;28(3):181-211.
10." Benson CB, Doubilet PM, Peters HE, Frates MC.
3." Bradley WG, Fiske CE, Filly RA. The double sac sign of Intrauterine fluid with ectopic pregnancy: a reappraisal. J
early intrauterine pregnancy: use in exclusion of ectopic Ultrasound Med. 2013;32(3):389-393.
pregnancy. Radiology. 1982;143(1):223-226.
11." Deaton JL, Honore GM, Huffman CS, Bauguess P. Early
4." Doubilet PM, Benson CB. Double sac sign and transvaginal ultrasound following an accurately dated
intradecidual sign in early pregnancy: interobserver reliability pregnancy: the importance of finding a yolk sac or fetal heart
and frequency of occurrence. J Ultrasound Med. 2013;32(7): motion. Hum Reprod. 1997;12(12):2820-2823.
1207-1214.
12." Stampone C, Nicotra M, Muttinelli C, Cosmi EV.
5." Sadek AL, Schiotz HA. Transvaginal sonography in the Transvaginal sonography of the yolk sac in normal and
management of ectopic pregnancy. Acta Obstet Gynecol abnormal pregnancy. J Clin Ultrasound. 1996;24(1):3-9.
Scand. 1995;74(4):293-296.
13." Tan S, Gulden Tangal N, Kanat-Pektas M, et al.
6." Richardson A, Gallos I, Dobson S, Campbell BK, Abnormal sonographic appearances of the yolk sac: which
Coomarasamy A, Raine-Fenning N. Accuracy of first-trimester can be associated with adverse perinatal outcome? Med
ultrasound in diagnosis of tubal ectopic pregnancy in the Ultrason. 2014;16(1):15-20.
absence of an obvious extrauterine embryo: systematic
review and meta-analysis. Ultrasound Obstet Gynecol. 14." Levi CS, Lyons EA, Zheng XH, Lindsay DJ, Holt SC.
2016;47(1):28-37. Endovaginal US: demonstration of cardiac activity in embryos
of less than 5.0 mm in crown-rump length. Radiology.
7." Marks WM, Filly RA, Callen PW, Laing FC. The decidual 1990;176(1):71-74.
cast of ectopic pregnancy: a confusing ultrasonographic
appearance. Radiology. 1979;133(2):451-454. 44

15." Berdahl DM, Blaine J, Van Voorhis B, Dokras A. 21." Doubilet PM, Benson CB, Bourne T, et al. Diagnostic
Detection of enlarged yolk sac on early ultrasound is criteria for nonviable pregnancy early in the first trimester. N
associated with adverse pregnancy outcomes. Fertil Steril. Engl J Med. 2013;369(15):1443-1451.
2010;94(4):1535-1537.
22." Hamilton BE, Martin JA, Osterman MJ, Curtin SC,
16." Gersak K, Veble A, Mulla ZD, Plavsic SK. Association Matthews TJ. Births: Final Data for 2014. Natl Vital Stat Rep.
between increased yolk sac diameter and abnormal 2015;64(12):1-64.
karyotypes. J Perinat Med. 2012;40(3):251-254.
23." Tong S, Caddy D, Short RV. Use of dizygotic to
17." Seungdamrong A, Purohit M, McCulloh DH, Howland monozygotic twinning ratio as a measure of fertility. Lancet.
RD, Colon JM, McGovern PG. Fetal cardiac activity at 4 1997;349(9055):843-845.
weeks after in vitro fertilization predicts successful completion
of the first trimester of pregnancy. Fertil Steril. 2008;90(5): 24." Akinboro A, Azeez MA, Bakare AA. Frequency of
1711-1715. twinning in southwest Nigeria. Indian J Hum Genet.
2008;14(2):41-47.
18." Doubilet PM, Benson CB. Embryonic heart rate in the
early first trimester: what rate is normal? J Ultrasound Med. 25." Ananth CV, Chauhan SP. Epidemiology of twinning in
1995;14(6):431-434. developed countries. Semin Perinatol. 2012;36(3):156-161.

19." Hertzberg BS, Mahony BS, Bowie JD. First trimester 26." Derom C, Gielen M, Peeters H, Frijns JP, Zeegers MP.
fetal cardiac activity. Sonographic documentation of a Time trends in the natural dizygotic twinning rate. Hum
progressive early rise in heart rate. J Ultrasound Med. Reprod. 2011;26(8):2247-2252.
1988;7(10):573-575.
27." Hall JG. Twinning. Lancet. 2003;362(9385):735-743.
20." Bracero LA, Seybold DJ, Witsberger S, Rincon L, Modak
A, Baxi LV. First trimester fetal heart rate as a predictor of 28." Hoekstra C, Zhao ZZ, Lambalk CB, et al. Dizygotic
newborn sex. J Matern Fetal Neonatal Med. 2016;29(5): twinning. Hum Reprod Update. 2008;14(1):37-47.
803-806.
29." Martin JA, Hamilton BE, Osterman MJ. Three decades of
twin births in the United States, 1980-2009. NCHS Data Brief.
2012(80):1-8.

45

30." Murphy MF, Hey K, Whiteman D, O'Donnell M, Willis B, 38." Tunon K, Eik-Nes SH, Grottum P, Von During V, Kahn
Barlow D. Is the natural twinning rate now stable? J Biosoc JA. Gestational age in pregnancies conceived after in vitro
Sci. 2000;32(2):279-281. fertilization: a comparison between age assessed from oocyte
retrieval, crown-rump length and biparietal diameter.
31." Lee KA, Oh KJ, Lee SM, Kim A, Jun JK. The frequency Ultrasound Obstet Gynecol. 2000;15(1):41-46.
and clinical significance of twin gestations according to 39." Kalish RB, Thaler HT, Chasen ST, et al. First- and
zygosity and chorionicity. Twin Res Hum Genet. 2010;13(6): second-trimester ultrasound assessment of gestational age.
609-619. Am J Obstet Gynecol. 2004;191(3):975-978.
40." Diagnostic Ultrasound. In: Rumack C, Wilson S,
32." American College of O, Gynecologists, Society for Charboneau JW, Levine D, eds. Overview of Obstetric
Maternal-Fetal M. ACOG Practice Bulletin No. 144: Multifetal Imaging. Vol One. 4th ed. Philadelphia: Mosby Elsevier;
gestations: twin, triplet, and higher-order multifetal 2011:1069-1125.
pregnancies. Obstet Gynecol. 2014;123(5):1118-1132.
46
33." Decker J. Mono-amniotic twins with true knot between
cords. Cent Afr J Med. 1976;22(7):137-138.

34." Roddie TW. Mono-amniotic twin pregnancy with twisting
of the cords; a case report. J Obstet Gynaecol Br Emp.
1957;64(5):724-725.

35." Suzuki S. Single Fetal Demise at 10 - 14 Weeks of
Monochorionic and Dichorionic Twin Pregnancy. J Clin Med
Res. 2016;8(4):331-333.

36." Blumenfeld YJ, Momirova V, Rouse DJ, et al. Accuracy
of sonographic chorionicity classification in twin gestations. J
Ultrasound Med. 2014;33(12):2187-2192.

37." Nyberg DA, Mack LA, Laing FC, Patten RM.
Distinguishing normal from abnormal gestational sac growth
in early pregnancy. J Ultrasound Med. 1987;6(1):23-27.

CHAPTER 5

Abnormal Intrauterine
Pregnancy

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

SECTION 1
Abnormal Intrauterine Pregnancy

KEY POINTS Pregnancy Failure (Movie 5.1)

1. Serum hCG level should not determine whether Nearly 80% of pregnancy failure occurs in the first trimester.
or not to 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 Congress of Obstetricians and Gynecologists (ACOG) defines
pregnancy 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 containing an embryo or fetus without fetal heart activity
rate of miscarriage of approximately 10% with within the first 12 6/7 weeks of gestation.(10) The most
higher rates associated with heavy vaginal common risk factors for pregnancy failure are advanced
bleeding and large subchorionic hemorrhage. maternal age and prior early pregnancy loss.(11) The risk for
(1,2) miscarriage, clinically recognized pregnancy loss, increases
five-fold when maternal age exceeds 40 years compared to
4. Sonographic criteria for completed miscarriage: maternal age between 20-29 years.(12)
endometrial thickness < 15 mm with no
evidence of retained products of conception. The thresholds for diagnosing pregnancy loss have come
(3-6) under scrutiny in the past several years. In addition to the
role of Beta-Human Chorionic Gonadotropin (hCG) levels
being questioned, sonographic findings for viable and

48

nonviable pregnancy have been brought into question. The placing patients at risk by terminating a desired viable
accepted numerical values for crown-rump length (CRL) pregnancy.(13)
without cardiac activity (5mm) and empty gestational sac (GS)
(16mm), originally thought to be 100 % specific for pregnancy When approaching the patient with possible pregnancy failure
the emergency physician needs to answer the following
GALLERY 5.1 Specificity and False Positive Rate of TV ultra- questions:

sound Findings of First Trimester Pregnancy Loss •" Where is the pregnancy?

Specificity and False Positive Rate (FPR) of TV ultrasound findings •" Is the pregnancy viable?
of first trimester pregnancy Loss (13,25)
•" Is this definite pregnancy failure, probable failure or
Diagnostic Findings of Pregnancy Specificity (Confidence Interval) False Positive Rate unlikely failure?
Loss
In order to answer these questions, the physician should use
CRL 5 mm and no FHR 100 % (90-100) 8.3 % the history and physical as well as diagnostic tools such as
ultrasound and hCG levels.
CRL 7 mm and no FHR 100 % (99) 0 %*
Beta-Human Chorionic Gonadotropin
GS 16 mm and no embryo 95 %(88-100) 4.4 %
HCG is a hormone released by the placenta in pregnant
GS 25 mm and no embryo 100 % (99) 0 % patients. This hormone is what is detected by urine and
serum pregnancy tests. Previous guidelines used a level of
*note Abdallah reports 0 % FPR with CRL >/= 5.3 mm and no FHR (25) 1000-2000 mIU/L international reference preparation (IRP) as
a discriminatory zone above which sonographic evidence of
Current sonographic criteria for first trimester pregnancy an intrauterine pregnancy was expected on transvaginal (TV)
loss are not 100% specific. ultrasound.(14-17)

failure, were found to have wide confidence intervals (Gallery The hCG level is usually present in the blood within 7 days of
5.1).(13 ) Current recommendations advise more generous fertilization and continues to rise throughout the first trimester
thresholds in diagnosing pregnancy failure in order to avoid before declining in the 2nd and 3rd trimesters. It has
commonly been thought to double every 48 hours during a

49