Although Rh immune globulin is commonly given to Rh-negative women undergoing genetic amniocentesis, there is little documentation of the necessity, efficacy, or safety of this policy. In this study, reproductive outcomes in 147 women each receiving 150 micrograms of Rh immune globulin after genetic amniocentesis were compared with those of an equal number of Rh-positive amniocentesis control women. No significant differences were found in the incidence of midtrimester pregnancy loss, mean gestational age at delivery, mean birth weight, or frequency of preterm deliveries (P greater than 0.05 for all parameters). While two antepartum stillbirths occurred in the study group and none in the control population, causes unrelated to Rh immune globulin administration were apparent for both fetal deaths (one multiple congenital anomaly syndrome, one abruptio placentae at 38 weeks). Of the 103 Rh-negative women giving birth to Rh-positive infants, none were overtly sensitized at the time of delivery. It is concluded that second trimester Rh immune globulin administration does not increase the risk of pregnancy loss.