Selective second-trimester termination of an abnormal fetus in twin pregnancies.

The probability of detecting a chromosomal or structural abnormality in one fetus of a dizygotic twin gestation is about twice that of the risk for a singleton. During the period January 1992 to October 1994 we performed selective termination of the abnormal fetus in 14 bichorionic twin gestations. Indications for selective termination were 10 structural abnormalities and 4 chromosomal abnormalities. The procedure was done at 14, 16, and between 20 and 25 weeks in 1, 2, and 11 cases, respectively. We had no pregnancy losses before 24 weeks' gestation. The mean gestational age at delivery was 34.2 +/- 3.9 (SD) weeks. In one case, severe abruptio placentae occurred and the neonate died. Thirteen neonates are alive and well. In five cases in which the procedure was done after 21 weeks' gestation, no decrease in the amount of amniotic fluid in the sac of the terminated fetus was observed. Our experience supports the general conclusion that selective termination for bichorionic abnormal twins is safe and effective.