Risk factors for perinatal human immunodeficiency virus transmission in patients receiving zidovudine prophylaxis

Objective: To identify modifiable obstetric factors associated with the fai lure of zidovudine chemoprophylaxis to prevent perinatal human immunodefici ency virus type 1 (HIV-1) transmission. Methods: We analyzed data from Pediatric AIDS Clinical Trials Group protoco l 076, a randomized, double-masked, placebo-controlled trial that demonstra ted that a zidovudine regimen could prevent perinatal HIV-1 transmission. W e estimated the zidovudine treatment effect using the relative reduction in transmission risk among women randomized to treatment with zidovudine comp ared with women randomized to receive placebo. Univariate and multivariate statistical analyses were used to assess whether the treatment effect diffe red in magnitude according to potential antepartum or intrapartum risk fact ors. Results: In the univariate analysis, the zidovudine treatment effect was fo und to differ significantly in magnitude according to quartile of maternal weight at the time of study entry (interaction test, P = .03); among women in the heaviest-weight quartile (weight more than 82 kg), there was a 26% r elative reduction in transmission risk, compared with a 79% relative reduct ion among the other three quartiles (interaction test, P = .05). In the zid ovudine treatment group, women who transmitted HIV-1 were significantly mor e likely than nontransmitters to have had antepartum procedures or conditio ns associated with increased risk of fetal exposure to maternal blood or ce rvicovaginal secretions (43% compared with 19%, P = .04). In the multivaria te analysis, adjustment for the plasma HIV-1 RNA level and CD4(+) cell perc entage did not eliminate the differential treatment effect according to the se factors. Conclusion: High maternal weight and conditions associated with fetal expos ure to maternal blood or cervicovaginal secretions may diminish the efficac y of zidovudine chemoprophylaxis. (Obstet Gynecol 1999;94:897-908. (C) 1999 by The American College of Obstetricians and Gynecologists.).