Diagnostic ultrasound ( PDFDrive )

CHAPTER 30 The First Trimester 1059
A
B
FIG. 30.12 Abnormal Amnion. (A) TVS at 9 weeks demonstrates an empty amnion within the gestational sac. This pregnancy eventually
failed. (B) Expanded amnion at 7 weeks. Note how the amnion is much larger than would be expected for an embryo (calipers) of this size. This
pregnancy did not progress.
FIG. 30.13 Normal 9-Week 4-Day Gestation. TVS shows the embryo
(calipers) and the amnion (arrow) separate from the surrounding chorion.
be fully visualized at the end of the ith week. Ragavendra et al. 48
placed a 12.5-MHz endoluminal catheter transducer into the
endometrial canal adjacent to the gestational sac. hey identiied
cardiac activity in an embryo with a CRL of 1.5 mm and resolved
the two walls of the heart, seen only as a tube. Using TVS, cardiac
activity is typically seen by the time an embryo is 2 mm in size,
and is almost always seen by 5-mm CRL. However, for strict
diagnosis of nonviable pregnancy the threshold is set at 7 mm
CRL. 4,5 Normal embryonic cardiac activity is greater than 100
beats per minute (bpm) (Video 30.1) when the embryo is less
than 6.3 weeks and 120 bpm at or beyond 6.3 weeks. 49 When
embryonic cardiac activity is visualized and the rate is less than
100 bpm, then follow-up should be obtained. We have seen
pregnancies with small embryos of 1–2 mm in size with heart
rates of 80–99 bpm with normal follow-up (see Fig. 30.15).
Umbilical Cord and Cord Cyst
he umbilical cord is formed at the end of the sixth week (CRL =
4.0 mm) as the amnion expands and envelops the connecting stalk,
the yolk stalk, and the allantois. he cord contains two umbilical
arteries, a single umbilical vein, the allantois, and yolk stalk (also
called the omphalomesenteric duct or vitelline duct), all of
which are embedded in Wharton jelly. he umbilical arteries
arise from the internal iliac arteries and in the newborn become
the superior vesical arteries and the medial umbilical ligaments.
he umbilical vein carries oxygenated blood from the placenta
to the fetus. he oxygenated blood is shunted through the ductus
venosus into the inferior vena cava and the heart. he single let
umbilical vein in the newborn becomes the ligamentum teres,
which attaches to the let branch of the portal vein. he ductus
venosus becomes the ligamentum venosum.
he allantois is associated with bladder development and
becomes the urachus and the median umbilical ligament. It
extends into the proximal portion of the umbilical cord. he
yolk stalk connects the primitive gut to the yolk sac. he paired
vitelline arteries and veins accompany the stalk to provide blood
supply to the yolk sac. he arteries arise from the dorsal aorta
to supply initially the yolk sac, then the primitive gut. he arteries
remain as the celiac axis, superior and inferior mesenteric arteries
supplying the foregut, midgut, and hindgut, respectively. he
vitelline veins drain directly into the sinus venosus of the heart.
he right vein is later incorporated into the right hepatic vein.
he portal vein is also formed by an anastomotic network of
vitelline veins.
he length of the umbilical cord has a close linear relationship
with gestational age in normal pregnancies. Hill et al. 50 found
they could reliably measure the cord lengths in 53 embryos at
6 to 11 weeks’ gestational age. Also, the cord lengths in 60% of
dead embryos were more than two standard deviations (2 SD)
below the value for that expected gestational age.
he width of the umbilical cord has also been measured
sonographically, and Ghezzi et al. 51 found a steady increase from
8 to 15 weeks. here was a signiicant correlation between cord