Left microtia in one monozygotic twin. A case report.

Monoamniotic twins are rare, with a double survival rate of only 40%. Congenital anomalies, while more common among twins in general, are particularly common in monoamniotic twins, with the increase principally the result of structural defects. Discordant phenotypes have been reported, but a malformation of the external ear in one twin has not. In a case of double survival of monoamniotic twins, one had left microtia and a single umbilical artery.