IMPACT OF ZIDOVUDINE USE ON RISK AND RISK-FACTORS FOR PERINATAL TRANSMISSION OF HIV

Objectives: To evaluate the impact of perinatal zidovudine use on the risk of perinatal transmission of HIV and to determine risk factors fo r transmission among women using perinatal zidovudine. Design: Prospec tive cohort study of 1533 children born to HIV-infected women between 1985 and 1995 in four US cities. Methods: The association of potential risk factors with perinatal HIV transmission was assessed with univar iate and multivariate statistics. Results: The overall transmission ri sk was 18% [95% confidence interval (CI), 16-21]. Factors associated w ith transmission included membrane rupture > 4 h before delivery [rela tive risk (RR), 2.1; 95% CI, 1.6-2.7], gestational age < 37 weeks (RR, 1.8; 95% CI, 1.4-2.2), maternal CD4+ lymphocyte count < 500 x 10(6) c ells/l (RR, 1.7; 95% CI, 1.3-2.2), birthweight < 2500 g (RR, 1.7; 95% CI, 1.3-2.1), and antenatal and neonatal zidovudine use (RR, 0.6; 95% CI, 0.4-0.9). For infants exposed to zidovudine antenatally and neonat ally, the transmission risk was 13% overall but was significantly lowe r following shorter duration of membrane rupture (7%) and term deliver y (9%). The transmission risk declined from 22% before 1992 to 11% in 1995 (P < 0.001) in association with increasing zidovudine use and cha nges in other risk factors. Conclusions: Perinatal HIV transmission ri sk has declined with increasing perinatal zidovudine use and changes i n other factors. Further reduction in transmission for women taking zi dovudine may be possible by reducing the incidence of other potentiall y modifiable risk factors, such as long duration of membrane rupture a nd prematurity.