Diagnostic ultrasound ( PDFDrive )

1066 PART IV Obstetric and Fetal Sonography
A
B
C
FIG. 30.21 Ultrasound Findings Suggestive of Early Pregnancy
Failure. (A) Irregular gestational sac (arrow), positioned low within the
uterus. No embryonic pole or yolk sac is present. On follow-up, the
patient had indings consistent with early pregnancy failure. (B) In another
patient, MSD of 21 mm without embryonic pole or yolk sac. Calipers
indicate sac measurement, but please note that they are improperly
placed and do not measure the greatest length in the image. The sac
is also irregular in shape and positioned low within the endometrial
cavity. The patient eventually underwent dilation and curettage with
pathologic indings consistent with early pregnancy failure. (C) In another
patient, worrisome indings include chorionic bump (long arrow) and
small marginal subchorionic hematoma (arrowheads).
Small Mean Sac Diameter in Relationship to
Crown-Rump Length
An additional feature that portends a higher likelihood of early
pregnancy failure is a small sac size in relationship to CRL.
Bromley et al. 75 found that in 16 patients at 5 1 2 to 9 weeks’
gestational age with an MSD less than 5 mm greater than the
CRL (i.e., MSD − CRL = <5 mm), sometimes termed early
oligohydramnios, 15 (94%) had spontaneous irst-trimester
abortion despite a normal heart rate for age (Fig. 30.22). As
noted by Giacomello, this is not truly “oligohydramnios” as the
small sac size is due to reduction of chorionic luid, outside of
the amnion. 76 A later study by Rowling demonstrated that this
inding may not be as ominous as originally thought, with at
least 35% of such cases progressing to the second trimester or
to a normal delivery. 73
Abnormally Large Amnion With Respect to
Embryo Size
he amnion is usually visualized ater the embryo, so it should
not be visualized in the absence of an embryo. 45 In normal
pregnancies, the amnion is not usually visible until the CRL of
the embryo is greater than approximately 7 mm. 77,78 A large visible
amniotic sac compared to the CRL is suggestive of abnormal
outcome. 45,79 Horrow 77 demonstrated that the diference between
the CRL and the amniotic sac diameter is 1.1 ± 2.0 mm in normal
embryos but 8.6 ± 3.8 mm in abnormal pregnancies. In abnormal
early pregnancies, the chorionic cavity remained appropriate in
size relative to the embryonic CRL, indicating that the increased
diference in CRL compared to amnion diameter is caused by
enlargement of the amnion rather than a small embryo. his
inding is especially useful in early embryos before visualization
of cardiac activity. As with other predictors of abnormal outcome,
patients with abnormal amnion appearance, either the “empty
amnion” 45 (Fig. 30.23) or “expanded amnion” 78,79 (Fig. 30.24,
Video 30.3) where the amnion is too large for an embryo of a
particular size, should be considered to have a nonviable pregnancy.
However, the expertise of the individual interpreting the
exam is important. If any question remains about viability of
the pregnancy, a follow-up ultrasound examination is prudent. 78
At times the clinician may see two sacs within the gestational
sac. Although it may be a monochorionic diamniotic pregnancy
(see Fig. 30.11), it may also be a failed pregnancy with an empty
amnion (or very small embryo with respect to the size of the
amnion) and a yolk sac (see Figs. 30.12B and 30.25).