The physiological changes that accompany gestation make women more susceptible to acquiring HIV during pregnancy than at any other time.1 According to a prospective study in Rakai, Uganda, pregnant women have significantly higher HIV incidence—2.3 infections per 100 person-years—than women who are breastfeeding and women who are neither pregnant nor breast-feeding (1.3 and 1.1 infections per 100 person-years, respectively). The rate of HIV acquisition is higher for pregnant women even after adjustment for such factors as the use of medical injections and the sexual risk behaviors of the women and their husbands.
The researchers sought to determine if the elevated rates of HIV acquisition during pregnancy found in earlier studies could be attributed to physiological changes related to pregnancy or increases in sexual risk behavior by the woman or her husband. Data were collected between 1994 and 1999 as part of a study of the control of STIs for prevention of HIV. Interviews were conducted at 10–12-month intervals with all consenting adults aged 15–49 living in rural communities in Rakai. The participants were asked to provide information on their age, marital status, educational level, health status, presence of genital ulcer disease, and number of sexual partners and level of condom use in the past year; blood samples were taken for HIV testing.
Sexually active women who were not pregnant or breast-feeding were tested for HIV at baseline and again at subsequent interviews; the average exposure interval contributed by these women was 0.97 person-years. If a woman was pregnant (determined by interview and physical examination or urine test), she was tested for HIV at the time the pregnancy was identified; the average interval of exposure during pregnancy was 0.38 person-years. Women who breast-fed their babies were tested again postpartum (average exposure interval, 1.05 person-years).
The analysis included 2,625 intervals of exposure during pregnancy among 2,188 women, 2,887 intervals of exposure during breast-feeding among 2,183 women and 24,258 intervals of exposure among 8,473 women who were neither pregnant nor breast-feeding. The intervals of pregnancy and breast-feeding were more likely than the intervals of nonpregnancy and non–breast-feeding to be contributed by women who were married, less educated and relatively young. For example, 91% of the intervals of exposure during pregnancy and during breast-feeding were contributed by married women, compared with 73% of the intervals when women were neither pregnant nor breast-feeding. This difference in proportion is highly significant, indicating that women experience spousal absence at lower rates during periods of pregnancy and breast-feeding than at other times.
Women had fewer sexual partners during intervals of pregnancy, and were less likely to use condoms during pregnancy than during intervals when they were neither pregnant nor breastfeeding. Condom use was less consistent during pregnancy than during periods of nonpregnancy and non–breast-feeding; genital ulcer disease was less common during pregnancy than during breast-feeding or during periods when women were neither pregnant nor breast-feeding. The proportion of women who had been exposed to medical injections varied little across the three groups (44–45%).
Multivariate Poisson regression models were used to estimate HIV incidence during pregnancy and breast-feeding relative to incidence during periods when women were neither pregnant nor breast-feeding. HIV incidence was highest among women aged 15–19, those aged 20–29, never-married women, previously married women, women who had multiple partners during the interval of exposure and those with genital ulcer disease. For almost all of the covariates examined (age, education, marital status, multiple sex partners, genital ulcers and condom use), HIV incidence was significantly greater during pregnancy than at any other time (2.3 infections per 100 person-years compared with 1.3 and 1.1 infections per 100 person-years for women who were breastfeeding and women who were neither pregnant nor breast-feeding, respectively). The HIV incidence ratio was significantly higher during pregnancy than during periods of nonpregnancy and non–breast-feeding (2.0); it was also higher during pregnancy than during periods of breast-feeding (1.8).
The husbands of married women were interviewed about their sexual risk behaviors; husbands were identified for 47–53% of cases across the three groups. The proportion of husbands who reported extramarital sexual partners was lower among those whose wives were pregnant than among those whose wives were breast-feeding or those whose wives were neither pregnant nor breast-feeding (36% vs. 40% and 39%, respectively). Among those reporting additional partners, men reported a lower mean number of sexual partners during intervals when their wives were pregnant than during intervals when their wives were neither pregnant nor breast-feeding.
In all three groups, 9–10% of HIV-negative women were married to HIV-positive men; the viral load of HIV-positive husbands varied little across groups. Within these relationships, HIV incidence was higher during pregnancy than at any other time, despite the fact that couples had a lower mean monthly frequency of intercourse during pregnancy than during breast-feeding or periods when women were neither pregnant nor breast-feeding.
The investigators conclude that women have a significantly higher risk of acquiring HIV during pregnancy than at any other time and that this heightened risk remains even after adjustment for behavioral factors. The researchers speculate that biology may play a role, through the structural or immunological changes induced by pregnancy. Although its results are not generalizable outside of Rakai, this study highlights an important public health issue for women and infants. The authors "believe that it would be prudent to warn women of this potential risk of HIV acquisition during pregnancy," and to encourage couples to practice monogamy, condom use or abstinence, which would also protect women from other STIs that could adversely affect pregnancy outcomes.
1. Gray RH et al., Increased risk of incident HIV during pregnancy in Rakai, Uganda: a prospective study, Lancet, 2005, 366(9492):1182–1188.