ABSTRACT
Compared with dichorionic (DC) twin pregnancies, monochorionic (MC) twin pregnancies (and higherorder multiple pregnancies (HOMPs) that are in part or entirely MC) have increased risks of serious complications, including fetal demise and prenatal injury to the brain, heart and kidneys (Table 27.1)1-6. This is the rationale for making the definitive diagnosis of chorionicity by ultrasound no later than 14 weeks into gestation (see Chapters 39 and 40). These increased risks are largely attributable to the fetal vascular structures of MC placentas (see Chapter 65).
