Multiple sexual partners and mother-to-child transmission of HIV-1

To investigate risk factors for mother-to-child transmission of HIV-1, particularly sexual behavior before and during pregnancy.

This study is part of a prospective cohort study in Butare, Rwanda, of 318 HIV-1-seropositive and 309 HIV-1-seronegative women enrolled during pregnancy and followed for a mean duration of 21 months (range, 8-34 months). Clinical follow-up of the mother-infant pairs was performed at 6-week intervals during the first year of life and at 4-month intervals thereafter. Detailed sexual history interviews were conducted during pregnancy and at the first postnatal visit.

Of 184 singleton infants born to HIV-1-infected mothers who survived the neonatal period, 32 (17%) children were classified as HIV-1-infected, 130 (71%) as not infected, and 22 (12%) died with indeterminate HIV-1 infection status. The vertical transmission rate was estimated to be between 20 and 29%. Unprotected sexual intercourse with increased number of partners during the past 5 years was strongly associated with mother-to-child transmission (P < 0.001), even after adjustment for maternal CD4/CD8 ratio, parity, history of sexually transmitted diseases, and evidence of genital infection during pregnancy. In a multivariate analysis, excluding children with indeterminate HIV-1 status, odds ratios for vertical transmission were 2.6 [95% confidence interval (CI), 1.0-6.9] for maternal CD4/CD8 ratio < 0.5 and 3.6 (95% CI, 1.1-11.8) for more than three sexual partners versus a single partner. Women with more than one sexual partner during the first trimester of pregnancy were at particularly high risk of transmitting the virus.

Unprotected sexual intercourse with multiple partners before and during pregnancy in a population with high HIV-1 seroprevalence may well increase the likelihood of HIV-1 transmission from an infected mother to her child.