Efficacy of antenatal zidovudine in reducing perinatal transmission of human immunodeficiency virus type 1. The New York City Perinatal HIV Transmission Collaborative Study Group.

New York City women (321) enrolled during 1986-1993 in an observational cohort study were analyzed retrospectively to determine the effectiveness of antenatal zidovudine in reducing perinatal transmission of human immunodeficiency virus type 1 (HIV-1) in women with various CD4+ lymphocyte counts (< 200, 200-499, > 499/microL). When CD4+ lymphocyte level was controlled for, women prescribed zidovudine during pregnancy were less likely to transmit HIV-1 to their infants (adjusted odds ratio, 0.36; 95% confidence interval, 0.14-0.92). There was no conclusive evidence that efficacy of zidovudine depended on CD4+ lymphocyte level, suggesting that women with severe CD4+ cell depression, who are at highest risk of transmitting HIV-1, may also benefit from zidovudine. Antenatal zidovudine treatment alone may substantially lower the risk of perinatal HIV-1 transmission. These data are consistent with the results of AIDS Clinical Trial Group protocol 076 and suggest that a substantial portion of zidovudine's protective effect may occur when used during the antenatal period.