196 Obstetrics and Gynecology Board Review •••
❍ What is different about the dividing membranes of DiMo versus DiDi twins?
In DiMo the separating membrane contains only two amnions only. In DiDi, the membrane contains chorion
(and thus blood vessels) as well.
❍ What early ultrasound finding is seen at the placenta-membrane junction with twin dichorionic placentas?
Lambda sign or “twin peak” sign.
❍ What type of cord insertions is more common in twin placentas?
Velamentous or marginal.
UMBILICAL CORD
❍ Name the types of cord insertion.
Centric, accentric, marginal, velamentous, furcated, and circumvallate.
❍ What is the term used to describe an umbilical cord insertion at the margin of the placenta?
Marginal insertion or “Battledore placenta.”
❍ What is the incidence of marginal insertion?
7%.
❍ What is a velamentous placenta?
Insertion of the cord into the membranes. Approximately 1% of singleton deliveries.
❍ What complications can arise from a velamentous placenta?
Vasa previa, thrombosis, rupture, and hemorrhage of vessels.
❍ What is a furcate cord insertion?
A cord that begins its branching to major stem vessels before it inserts into the placenta and is not covered by
Wharton jelly.
❍ What are some complications are associated with furcate cord insertion?
Thrombosis and fetal hemorrhage.
❍ What is a circumvallate insertion?
An incomplete covering of the basal plate of the placenta by the fetal membranes. A central depression and ring is
formed at the attachment site of the membranes.
❍ What is significant about a circumvallate insertion?
It is associated with abruption, hemorrhage, premature rupture of membranes (PROMs), and congenital
malformations.