Increased risk of incident HIV during pregnancy in Rakai, Uganda: a prospective study

Summary

Background

HIV acquisition is significantly higher during pregnancy than in the postpartum period. We did a prospective study to estimate HIV incidence rates during pregnancy and lactation.

Methods

We assessed 2188 HIV-negative sexually active women with 2625 exposure intervals during pregnancy and 2887 intervals during breastfeeding, and 8473 non-pregnant and non-lactating women with 24 258 exposure intervals. Outcomes were HIV incidence rates per 100 person years and incidence rate ratios estimated by Poisson multivariate regression, with the non-pregnant or non-lactating women as the reference group. We also assessed the husbands of the married women to study male risk behaviours.

Findings

HIV incidence rates were 2·3 per 100 person years during pregnancy, 1·3 per 100 person years during breastfeeding, and 1·1 per 100 person years in the non-pregnant and non-lactating women. The adjusted incidence rate ratios were 2·16 (95% CI 1·39–3·37) during pregnancy and 1·16 (0·82–1·63) during breastfeeding. Pregnant women and their male partners reported significantly fewer external sexual partners than did the other groups. In married pregnant women who had a sexual relationship with their male spouses, the HIV incidence rate ratio was 1·36 (0·63–2·93). In married pregnant women in HIV-discordant relationships (ie, with HIV-positive men) the incidence rate ratio was 1·76 (0·62–4·03).

Interpretation

The risk of HIV acquisition rises during pregnancy. This change is unlikely to be due to sexual risk behaviours, but might be attributable to hormonal changes affecting the genital tract mucosa or immune responses. HIV prevention efforts are needed during pregnancy to protect mothers and their infants.

Introduction

An observational study in Malawi showed that rates of HIV acquisition are significantly higher during pregnancy than in the postpartum period,1, 2 and data from Rakai, Uganda, suggested similar trends, but differentials in HIV incidence between pregnant and postpartum women were not significant.2, 3 However, neither study adjusted for behavioural factors that can affect HIV acquisition. Women might be at increased risk of HIV during pregnancy because of their own or their partner's sexual behaviours, or because of the physiological changes during gestation. Irrespective of the mechanism of heightened risk, these findings have important implications for HIV prevention, both to protect mothers from primary HIV infection during pregnancy and to potentially avoid mother-to-child HIV transmission, which can be increased by the rise in HIV-1 viraemia associated with recent maternal infection.⁴

To address these issues we assessed the incidence rate of HIV during pregnancy and lactation, and compared this to the incidence rate of HIV during periods of non-pregnancy and non-lactation using longitudinal data from a community cohort in Rakai, Uganda. We postulated that if the incidence rate of HIV acquisition during pregnancy remained raised after adjustment for characteristics and behaviours, physiological changes of pregnancy might be responsible for any differences in incidence rates recorded during pregnancy, lactation, and non-pregnancy and non-lactation periods.