Dichorionic Diamniotic Twin Placenta

Twin pregnancies may be monozygotic or dizygotic. When two fertilized ova implant near each other (dizygotic), the two placentas may show partial fusion. Examination of the membranes will show two chorions and two amnions (dichorionic diamniotic). If a single fertilized ovum divides within two days of fertilization, it will develop into two embryos (monozygotic) each with its chorion and amnion. Therefore, examination of a dichorionic diamniotic placenta alone cannot distinguish between monozygotic and dizygotic twins. Image courtesy of Dr. Jean-Christophe Fournet, Paris, France; humpath.com; Used with permission