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Background:  An annual residual mother-to-child HIV-1 transmission (MTCT) rate of 1 to 2% persists in the French Perinatal Cohort. Although MTCT was high among women who did not receive ART, 96% of HIV-1-infected women, enrolled in the period 1997 to 2002, received ART during their pregnancy and accounted for 80% of the cases of MTCT. The objective of this study was to identify factors associated with HIV-1 transmission among treated women.

Methods:  HIV-1-infected women delivering between January 1, 1997 and December 31, 2002 in the 77 sites of the French Perinatal Cohort were included for this analysis if they received ART during pregnancy and did not breast-feed (n = 3801).

Results:  MTCT was strongly correlated with late access (third trimester) to specialized care (p < 0.001), with high plasma HIV-1 RNA (³ 1000) closest to the delivery (p < 0.001) and with preterm (before 37 weeks) delivery (p = 0.03). MTCT occurred in 2.6% (13 of 509) of premature infants versus 1.3% (43 of 3292) of full-term infants. Among full-term infants, the rate of MTCT was 0.7% (15 of 2207) if the mother’s HIV-1 RNA was < 1000 copies/mL and was 2.9% (28 of 968) if the mother’s HIV-1 RNA was ≥ 1000 copies/mL. In the latter case, the lack of intrapartum therapy was significantly associated with a higher risk of transmission after adjustement, in a logistic regression, for HIV-1 RNA level (≥ 10,000 vs 1000 to 10,000), mode of delivery, gestational age at the start of ART, number of drug changes during pregnancy, last sequence of ART (zidovudine [AZT] alone, 2 NRTI, or HAART), and mother’s geographic origin:  adjusted OR 2.8 (95% CI 1.1 to 7.0). Intrapartum therapy was intravenous AZT, exclusively in most cases, or associated with single dose nevirapine [NVP] (7%). Only 5% of women did not receive any intrapartum therapy. Moreover, the lack of maternal intrapartum therapy remained associated with MTCT whatever the type of neonatal prophylaxis (AZT alone or with another NRTI).

Conclusions:  MTCT increased with late access to specialized care, RNA level, and preterm delivery. In full term neonates born to treated mothers whose last HIV-1 RNA was > 1000 copies/mL, the lack of intrapartum prophylaxis appeared to be independently associated with a higher risk of MTCT.

Keywords: mother-to-child transmission; cohort studies; HIV-1