Diagnostic ultrasound ( PDFDrive )

CHAPTER 43 Sonographic Evaluation of the Placenta 1467
A
B
C D E
FIG. 43.2 Normal Appearance of Placenta. (A) At 18 weeks, note the uniformly echogenic appearance of the placenta. (B) Note marginal
sinus of placenta (arrow), a circumferential venous drainage point into the maternal uterine veins that should not be mistaken for placental separation.
(C) Placental lake (arrow) at 20 weeks. See also Video 43.1. (D) Placenta at 32 weeks’ gestation. Note the diffuse placental calciications.
(E) Placenta at 39 weeks’ gestation with deined linear calciications outlining the placental cotyledons. Note the increasing echogenicity in the
placenta as it matures.
weight and birth weight, but they have not been shown to predict
the development of preeclampsia. 18,19 he irst-trimester placental
volume quotient (placental volume/crown-rump length) is low
for aneuploid fetuses, with 53% having a quotient less than 10th
percentile. 20 For twins, the placental volume is 83%, and for
triplets 76%, that of singletons, for a given gestational age. 21
he placenta dramatically increases in size until approximately
15 to 17 weeks’ gestation. From this point, there is a fourfold
increase in placental size until delivery, whereas over this same
time period the fetus has a 50-fold increase in size. 22 Midtrimester
placental volume is associated with maternal nutritional status,
birth weight, and pregnancy outcome. 23-27
FIG. 43.3 Thick Placenta in Fetal Hydrops. The calipers indicate
how one would measure the thickness of the placenta. Note the ascites
(arrow). See also Video 43.2 for thick placenta in fetus with villitis.
Placental Vascularity and
Doppler Ultrasound
he human placenta is a discoidal, villous, hemochorial structure.
Nutrients are exchanged over many villi. Surrounding the villi
are the intervillous spaces, which are bathed in maternal blood.
he villi are sproutlike projections from the chorionic plate into
the intervillous space. he villi are directly connected to the fetal
vascular system, whereas the maternal blood emanates from the
developing spiral arteries to the intervillous spaces to contact