Is zidovudine therapy in pregnant HIV-infected women associated with gestational age and birthweight?

Objective: Prophylactic zidovudine during pregnancy and labour reduces mate rnal viral load and, with neonatal therapy, has been shown to reduce vertic al transmission. However, zidovudine may have additional effects. Advanced HIV disease is associated with premature delivery, which in turn results in increased vertical transmission. Data from the European Collaborative Stud y (ECS) were analysed to investigate whether zidovudine could be associated with decreased prematurity risk and/or with a reduced frequency of low bir thweight. Methods: HIV-infected pregnant women enrolled in the ECS were followed pros pectively according to a standard protocol. Gestational age was assessed by ultrasound, prematurity was defined as delivery before 37 weeks and the cu t-off for low birthweight was 2500 g. We calculated odds ratios (OR) to est imate the effect of zidovudine on the risk of premature or low birthweight delivery. Results: In 2299 mothers, zidovudine taken to reduce the risk of vertical t ransmission decreased the odds of premature delivery by a quarter (OR = 0.7 6, 95% confidence interval (CI) 0.53-1.09), and the odds of low birthweight by nearly half (OR = 0.55, 95% CI 0.39-0.79). Allowing for CD4 count and m ode of delivery did not greatly alter these OR values. A multivariate analy sis suggested that prophylactic zidovudine and prematurity were independent ly associated with risk of transmission. Conclusion: Our findings suggest an additional health benefit of zidovudine . Even ii most vertical transmission occurs around the time of delivery, th erapy earlier in pregnancy could have an indirect effect on transmission ra tes through delaying delivery. This hypothesis needs to be confirmed or ref uted by more appropriate studies.