Discordant amniotic band sequence in monozygotic twins.

Multiple congenital anomalies were identified at 16 weeks gestation in one fetus of an unsuspected twin pregnancy while ultrasound examination was performed before routine genetic amniocentesis. Further sonographic studies documented the amniotic band sequence (ABS) and transient oligohydramnios in the affected fetus. The latter finding supports the theory of amnion rupture followed by amniotic fluid leakage through an ineffective chorion barrier as the pathogenesis of compression related anomalies in this syndrome. Extensive craniofacial involvement including hydrocephalus, encephalocele, and multiple facial clefts in the affected fetus, combined with an erroneous ultrasound diagnosis of ABS in the unaffected twin, created an extremely difficult management and counseling situation. A review of ABS, the embryology of placental membrane development, and a discussion of selective termination procedures are presented.