Prenatal diagnosis by chorionic villus sampling in multiple pregnancies prior to fetal reduction.

Ovulation induction and assisted-reproduction techniques have dramatically increased the incidence of high-risk multiple pregnancies over the past 10 years. Perinatal outcome may be improved by the use of multifetal reduction. The fetus to be reduced used to be selected only on technical grounds. We report on the results of prenatal diagnosis by chorionic villus sampling (CVS) during the first trimester in 32 multifetal pregnancies in which fetal reduction was requested. The mean gestational age at CVS was 10.5 weeks. Chromosomal analyses were available for all sampled fetuses, three of which were chromosomally abnormal. In 24 couples, fetal reduction to twin pregnancies was successfully carried out within 1 week after the CVS. In seven cases, the couples elected not to proceed with fetal reduction after receiving information that the chromosomal analysis was normal in all fetuses. Mean gestational ages at delivery were, respectively, 34.6 and 31.8 weeks in the reduced and the nonreduced groups (p = 0.04). No fetal losses occurred in either group; one neonatal death was observed after a preterm delivery because of preeclampsia in a twin pregnancy. Prenatal cytogenetic diagnosis during the first trimester in multiple pregnancies prior to fetal reduction appears to be feasible, accurate, and safe. Abnormal chromosomal results indicate the fetus(es) to be reduced. The parents' decisions not to proceed with the fetal reduction procedure, where chromosomal results in all the fetuses were normal, were unexpected.