••• Chapter 19^ The Placenta and Umbilical Cord^195
MULTIPLE GESTATION
❍ Name the two types of twin placentation.
Monochorionic and dichorionic.
❍ What zygosity is associated with each?
Monochorionic placentas are always monozygotic twins. Dichorionic placenta can have monozygotic (DiMo) or
dizygotic (DiDi) twins.
❍ What further differentiation can be made of monochorionic placentas?
Monoamnionic versus diamnionic.
❍ Which type of twinning has the highest morbidity?
Monoamnionic monochorionic.
❍ What feature of only monochorionic placentas leads to twin-twin transfusion syndrome?
Arteriovenous anastomoses.
❍ What is the recommended method of delivery for mono-mono twins?
Cesarean delivery.
❍ What is the biggest mortality risk of mono-mono twins?
Cord entanglement.
Cord entanglement seen with mono-mono twins. Photo courtesy of Abington Memorial Hospital, Abington, PA.