HIV-1 infection in a population-based twin sample

Objective: To examine factors associated with perinatal HIV-1 transmission among twins. Methods: We identified twins delivered by a population-based cohort of HIV-infected mothers on New York State Medicaid. Tested algorithms were applied to Medicaid files to identify HIV infection in mothers and twins. The HIV transmission rate 3 years after delivery was assessed from Kaplan-Meier curves. Proportional hazards models with adjustment for twin clustering were used to determine the relative hazard (RH) of transmission. Results: In 35 twin pairs, transmission was 20.5%. The risk of transmission was increased significantly for advanced maternal HIV infection (rh = 10.8, 95% confidence interval 2.11, 54.9). We found no association of birth order with twin HIV status. Conclusions: These data suggest that maternal stage of disease plays a greater role in vertical HIV transmission than birth order. To prevent material-child HIV transmission, reducing maternal viral load is likely to have a greater impact than modifying delivery factors.