Diagnostic ultrasound ( PDFDrive )

CHAPTER 43 Sonographic Evaluation of the Placenta 1485
A
B
FIG. 43.31 Normal Cord Insertion Into Placenta. (A) Gray-scale sonogram demonstrates a normal umbilical cord insertion into the placenta.
(B) Color Doppler sonogram shows the umbilical cord insertion into the placenta. See also Video 43.16.
neonatal death, retained placenta ater delivery, and postpartum
hemorrhage. 167,170,171 Marginal umbilical cord insertions are not
associated with IUGR or preterm delivery 172 but are associated
with vasa previa.
he insertion of the umbilical cord into the membranes leads
to the unsupported coursing of the umbilical vessels to the
placental disc and many complications. Wharton jelly supports
and protects the umbilical vessels in the umbilical cord. With
the vessels in the membranes, no Wharton jelly is present, leading
to increased risk of compression or even rupture of these vessels.
Intrapartum fetal heart rate patterns show more variable decelerations
and no accelerations with velamentous cord insertions
during the irst and second stages of labor compared to controls. 170
Increasing length of the unsupported membrane vessels is associated
with increasing rates of abnormal heart rate patterns, as is
the umbilical cord insertion being in the lower portion rather
than the middle or upper portion of the uterus. 170 Nonreassuring
fetal heart rate patterns and emergency cesarean deliveries are
more frequent with velamentous cord insertions in the lower
third than in the middle or upper third of the uterus. 170 Because
velamentous cord insertions are typically located low in the uterus,
TVS can be critical to making this diagnosis.
A rare abnormality of umbilical cord insertion that overlaps
with velamentous umbilical cord insertions is furcate umbilical
cord insertion. his occurs when the umbilical cord vessels
prematurely divide and insert into the membranes with vessels
coursing to the placental substance (Fig. 43.34). he mangrove
sign, so called because of the roots of a mangrove tree having a
similar appearance, has been coined to denote furcate umbilical
cord insertions. 173 A recent case report documents the association
of a furcate umbilical cord insertion with retained placenta and
a fetal syndrome. 174 Further research is necessary to better
understand this rare entity.
Vasa Previa
Vasa previa is the situation where the umbilical cord vessels
overlie the internal cervical os (Fig. 43.35, Video 43.17). he
incidence is approximately 0.6 in 1000 pregnancies, 175 but
approximately 25% that are diagnosed in the second trimester
resolve. 176 Because these are fetal vessels, even a small amount
of blood loss from rupture of these vessels can lead to fetal death.
High-risk situations that require speciic exclusion of vasa previa
include velamentous umbilical cord insertions in which the
membranous fetal umbilical vessels can traverse the internal
cervical os somewhere along their length. Marginal umbilical
cord insertions, especially those with aberrant vessels within the
membranes, also are associated with vasa previa. 177 Presence of
bilobed placentas 178 or the more common succenturiate lobes 179
requires that a vasa previa be excluded, given the potential for
a poor neonatal outcome. Prior low placenta, placenta previa,
multiple gestations, pregnancies resulting from in vitro fertilization,
and pregnancies with umbilical cord insertions occurring
in the lower third of the uterus in the irst trimester are all
associated with vasa previa. 175,177,179,180
Once a vasa previa is diagnosed, obstetric management is
critical to optimize outcome. Current recommendations are
for antenatal corticosteroids between 28 and 32 weeks’ gestation,
consideration of hospitalization between 30 and 34 weeks’
gestation, and delivery at 34 to 37 weeks’ gestation, which is
recommended to obviate the risks of vessel rupture that can
occur with labor or rupture of the membranes. 181 If the patient
has preterm labor, ruptured membranes, or bleeding before
35 weeks, delivery at the earlier gestational age should be
considered. 180,182
Vasa previa is diagnosed when a fetal vessel is identiied
overlying the internal cervical os. Although gray-scale ultrasound