Is the risk of mother-to-child transmission of HIV higher among female compared with male infants? A case of Rakai, Uganda

Purpose: To assess gender differences in the risk of mother-to-child transmission (MTCT) of human immunodeficiency virus (HIV). HIV-positive mothers were identified from a population cohort followed from 1994 to 2000. HIV infection in mothers was detected using two independent enzyme immunoassays and infant HIV infection was diagnosed using RNA- polymerase chain reaction. Birth weight was determined by anthropometry. Logistic regression was used to assess the univariate and multivariate risk factors of MTCT. Approximately 16% of 371 infants were HIV-positive in the in-utero and intrapartum periods and an additional 16% were infected via breastfeeding. Female infants were significantly more likely to be HIV infected perinatally compared with male infants (20.8% vs. 12.4%, respectively, P = 0.035), but there was no significant sex differences in postnatal risk of MTCT. In adjusted analyses, among mothers with higher than median HIV viral loads, there was no significant difference in the risk of MTCT by gender, but among mothers with lower than median HIV viral loads, female infants were significantly more likely to be HIV infected (odds ratio = 4.1, confidence interval = 1.04-16.1). Low birth weight was more frequent in female than male infants born to HIV-positive mothers. Female infants could be more susceptible to HIV infection in the in-utero and peripartum period compared with male infants. Alternatively, this sex association could be due to higher in-utero mortality rates of male infants or to increased susceptibility of female infants.