Risk factors for in utero and intrapartum transmission of HIV.

Objective: To identify predictors of in utero and intrapartum HIV-1 transmission in infants born in the Women and Infants Transmission Study between 1990 and 2000.

Methods: In utero HIV-1 infection was defined as an infant with the first positive HIV-1 peripheral blood mononuclear cell culture and/or DNA polymerase chain reaction assay at 7 days of age or younger; intrapartum infection was defined as having a negative HIV-1 culture and/or DNA polymerase chain reaction assay at 7 days of age or younger and the first positive assay after 7 days of age.

Results: Of 1709 first-born singleton children with defined HIV-1 infection status, 166 (9.7%) were found to be HIV-1 infected; transmission decreased from 18.1% in 1990-1992 to 1.6% in 1999-2000. Presumed in utero infection was observed in 34% of infected children, and presumed intrapartum infection, in 66%. Among infected children, the proportion with in utero infection increased over time from 27% in 1990-1992 to 80% (4 of 5) in 1999-2000 (P = 0.072). Maternal antenatal viral load and antiretroviral therapy were associated with risk of both in utero and intrapartum transmission. Controlling for maternal antenatal viral load and antiretroviral therapy, low birth weight was significantly associated with in utero transmission, while age, antenatal CD4 cell percentage, year, birth weight, and duration of membrane rupture were associated with intrapartum transmission.

Conclusion: Although there have been significant declines in perinatal HIV-1 infection over time, there has been an increase in the proportion of infections transmitted in utero.