The outcome of twin pregnancies discordant for trisomy 21.

The management of twin pregnancies discordant for trisomy 21 is dependent on the gestation at diagnosis, chorionicity, and parental preference. Our experience with the management of 15 cases in 1,839 twin pregnancies over a 12-year period is described. Selective termination is not always associated with a successful outcome for the normal co-twin. Two of the three monochorionic twin pregnancies affected by trisomy 21 were discordant. Amniocentesis should be strongly considered rather than chorionic villus sampling in monochorionic twin pregnancies. Pregnancies that continue with a trisomy 21 affected fetus are at risk of polyhydramnios and premature labor.