Diagnostic Ultrasound - Abdomen and Pelvis

Failed First Trimester Pregnancy
TERMINOLOGY
Definitions
• Failed first trimester pregnancy refers to collection of
specific diagnoses that are nonviable
○ Avoids confusion and simplifies terminology
• Anembryonic pregnancy (AP): Failure of embryo to develop
or early demise with resorption of embryonic pole (a.k.a.
"blighted ovum," less favored term)
• Embryonic demise (ED): Embryo ≥ 7 mm in length with no
heartbeat
• Spontaneous abortion: Involuntary pregnancy loss in 1st 20
weeks; may be inevitable, incomplete, or complete
• Missed abortion: General term for ED or AP; latter terms
are more accurate and preferred
IMAGING
General Features
• Intrauterine pregnancy (IUP) with abnormal features that
will not result in a live birth (nonviable)
○ e.g., lack of embryonic development, lack of embryonic
cardiac activity, or abnormal-appearing passing
gestational sac (GS)
Ultrasonographic Findings
• Grayscale ultrasound
○ Empty sac: Gestational sac with no embryo ± YS
– Empty amnion sign: GS with visible amnion, without
visible embryo
– Specific sign of anembryonic gestation when mean
sac diameter (MSD) ≥ 25 mm
□ Embryo usually seen at MSD of 18 mm (old criteria);
however, not absolute
□ Lack of embryo with MSD 18-25 mm is worrisome
and should prompt follow-up US in 2 weeks
□ Empty sac (i.e., no YS or embryo) on 2 scans
performed 14 days apart is definitive for failed
pregnancy
○ Abnormal embryo
– Expanded amnion sign: Visible amnion surrounding
embryo with no heartbeat
– Cardiac activity is usually visible when embryo is seen
– However, lack of cardiac activity at cutoff of 7 mm for
crown rump length (CRL) is criterion for embryonic
demise
– No cardiac activity at CRL < 7 mm is worrisome for
failed IUP and should prompt follow-up US
○ Spontaneous abortion
– Inevitable: GS herniating into or located centrally in
cervical canal with open internal os
– Incomplete or in progress: Heterogeneous
endometrial thickening ± color Doppler flow, ± open
cervical os
– Complete: Thin, undistorted endometrial stripe
□ Indistinguishable by US from ectopic or early
nonvisualized IUP
□ Conclusive if prior documentation of IUP
○ Other findings that may indicate poor prognosis
– Abnormal yolk sac (YS) typically seen when MSD ≥ 10
mm (5 1/2 week gestation)
□ Normal YS is smooth, round, echogenic, < 6 mm
□ Abnormal features: Pyknotic (collapsed), calcified,
or large YS → poor prognosis
□ Yolk stalk sign with YS distant from embryo
– Irregular sac contour (e.g., angular or amoeboid
shape)
– Small sac size relative to embryo: < 5 mm difference
between MSD and CRL
– Poorly echogenic decidua ± cystic change
– Abnormal GS location positioned low in uterus
– Perigestational hemorrhage (a.k.a. subchorionic
bleed)
□ Crescentic collection; echogenicity depends on age;
usually anechoic or hypoechoic
□ Small (< 20% sac circumference): Common; often
self-limited; > 90% pregnancy success when living
embryo present
□ Large (> 50% sac circumference): ↑ risk pregnancy
loss (20% with living embryo)
• Color Doppler
○ Not necessarily useful: Variable findings and carries
theoretical risks to developing embryo due to heating;
use with caution to support abnormal diagnosis
○ May see poor color Doppler signal around gestation sac
Imaging Recommendations
• Use magnified views to look carefully for yolk sac and
embryo, and avoid missing multiple gestations
• Use M-mode US or video clips to document cardiac activity
and M-mode to measure rate
• Correlate findings with clinical presentation and human
chorionic gonadotropin (hCG) levels to guide interpretation
and recommendations
○ Use caution in interpreting single hCG measurement,
does not reliably distinguish viable/nonviable IUP from
ectopic pregnancy
DIFFERENTIAL DIAGNOSIS
Normal Early Intrauterine Pregnancy (IUP)
• GS appears at ~ 5 weeks: Smooth, round or oval, fundal, ±
intradecidual sac sign (IDSS) or double sac sign (DSS)
○ IDSS: Eccentric fluid collection in decidua, echogenic rim,
curved edges
○ DSS: Concentric echogenic bands around most of GS
○ Signs absent in ≤ 35% of GS
○ Helpful if seen; however, absence does not exclude IUP
○ Normal IUP still possible if MSD 18-25 mm but no
YS/embryo
• Prominent color flow around sac: Low resistance, high
velocity on spectral analysis of chorion
○ Variable and not necessarily useful, especially given
theoretical risks to normal IUP with Doppler imaging
Pseudosac of Ectopic Pregnancy (EP)
• Tear drop-shaped fluid collection, centrally located, with no
IDSS or DSS
• Nonspecific intrauterine fluid collection is more likely to be
GS (normal or abnormal) than pseudogestational sac of
ectopic pregnancy (seen in < 20% of EP)
• Search for specific findings (e.g., tubal ring in adnexa)
• Consider follow-up imaging in stable patient with
indeterminate scan
Diagnoses: Female Pelvis
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