Virus load in pregnancy and its relation to mother-to-child human immunodeficiency virus (HIV) transmission were studied prospectively. From 1989 to 1994, 320 HIV-infected women from 18 centers had plasma samples stored. Among women not receiving antiretroviral therapy, the polymerase chain reaction RNA level was 3.6 log at delivery, and 15% of women had levels below the detection limit. There was no variation during pregnancy. Women born in sub-Saharan Africa had lower RNA levels, although their CD4 cell distribution did not differ from that in other women. Among 236 evaluable children, 19% ± 5% were infected. Transmission occurred in 12% of cases (confidence interval, 5%–22%) with < 1000 copies/mL versus 29% ± 10% of those with >10,000 copies/mL (P < .02). Maternal virus load appears strongly related to HIV transmission to the child.

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SEROGEST Cohort Group*