Incident HIV infection in pregnant and lactating women and its effect on mother-to-child transmission in South Africa.

We described HIV incidence and mother-to-child transmission (MTCT) among women during pregnancy and lactation. Forty-eight (3.4%) of 1396 women seroconverted during pregnancy or <12 mo after delivery. This group of HIV-exposed children was at 2.3 times higher risk of infection (MTCT 20.5% [8 of 39] vs 9.0% (83 of 925]). An estimated 20% with CD4+ cell counts <350 would have been eligible for antiretroviral therapy (ART), yet all women with incident HIV infections are more likely to transmit HIV to their children. To ensure optimal prevention of MTCT, all women who seroconvert during pregnancy or lactation should be considered for ART for the purpose of prevention of MTCT, and women with CD4+ <350 should continue to receive ART.