An observational study of vertical transmission when the mother but not the infant received oral zidovudine

Objective; To examine the rate of vertical transmission from HIV-1 infected women who were treated with zidovudine (ZDV) during their pregnancies, but whose infants were not treated with ZDV. Methods: Data from all HIV-1 infected pregnant women followed prospectively prior to February 1994 at 5 university HIV clinics who were prescribed ZDV during pregnancy were included in this study. The following variables were analyzed: effect of intravenous ZDV; number of weeks of ZDV during pregnancy, continuity of ZDV usage; maternal demographics, length of gestation, type of delivery and CD4 values. Results: One hundred and eighty-eight women and 190 infants (two pairs of twins) were deluded in the study.Treatment practices and demographics varied between sites. Overall 20% of the women had CD4 counts dose to delivery of <200. Seventy-three percent of the infants were delivered vaginafly with 12.256 bom at <37 weeks gestation. The women took ZDV for a mean duration of 14.2 weeks during gestation with 15.656 receiving intravenous ZDV during labor.Those receiving intravenous ZDV during labor received a mean of 493 mg over a mean of 8.1 hours. None of the infants were treated with ZDV after birth. HIV-I infection status is unknown for 11 of the infants. Among the remaining motherinfant pairs there were 22 infected infants, a vertical transmission rate of 12.4% (CI 8.0-18.236). Variation in transmission rates between sites could have occurred by chance (by DerSimonian and Laird's and Fisher's exact tests). Except for a trend towards decreased transmission among women who received intravenous ZDV during labor and increased transmission among women with CD4 counts <200. no clinical or treatment variables were associated with the rate of vertical transmission. Conclusions: The results of this observational study suggest that the use of ZDV in pregnancy apart form the treatment of the infant after birth can lower the vertical transmission rate of HIV-I when compared to untreated women observed in other studies (2656 in ACTG 076). Further studies are indicated to determine the role of neonatal ZDV treatment of HIV-1 exposed infants.