Date Published: October 17, 2018
Publisher: Public Library of Science
Author(s): Milly Marston, Basia Zaba, Jeffrey W. Eaton, Philip Anglewicz.
Projections of fertility of HIV positive women as ART scales up are needed to plan prevention of mother-to-child transmission (PMTCT) services. We describe differences in exposure to pregnancy between HIV positive and HIV negative women by age, region and national ART coverage to evaluate the extent to which behavioural differences explain lower fertility among HIV positive women and assess whether exposure to pregnancy has changed with antiretroviral treatment (ART) scale-up.
We analysed 46 nationally representative household surveys in sub-Saharan Africa conducted between 2003 and 2015 to estimate risk of exposure to recent sex and pregnancy of HIV positive and HIV negative women by age using a log binomial model. We tested for regional and urban/rural differences and associations with national ART coverage. We estimated an adjusted fertility rate ratio of HIV positive to HIV negative women adjusting for differences in exposure to pregnancy.
Exposure to pregnancy differs significantly between HIV positive and negative women by age, modified by region. Younger HIV positive women have a higher exposure to pregnancy than HIV negative women and the opposite is true at older ages. The switch occurs at 25–29 for rural women and 30–34 for urban women. There was no evidence that exposure to pregnancy of HIV positive women have changed as national ART coverage increased. The inferred rate of fecundity of HIV positive women when adjusted for differences in exposure to pregnancy were lower than unadjusted fertility rate ratios in women aged 20–29 and 20–24 in urban and rural areas respectively varying between 0.6 and 0.9 over regions.
The direct effects of HIV on fertility are broadly similar across ages, while the dramatic age gradient that has frequently been observed is largely attributable to variation in relative sexual exposure by age.
Numerous studies have demonstrated that the relationship between HIV and fertility varies with age. Among the youngest women aged 15–19 years, fertility is higher among HIV positive women, while above age 25 the fertility of HIV positive women becomes increasingly lower than that of their HIV negative counterparts, termed ‘HIV associated subfertility [1–3]. Population based studies have also identified differences in HIV subfertility by region [3,4], urban and rural area  and speculated whether changes are associated with increased antiretroviral treatment (ART) roll out [3, 5, 6].
Fig 1 describes a conceptual framework for the possible effects of HIV on fertility. In this analysis, we aim to estimate the extent to which lower fertility is attributable to lower exposure to pregnancy due to behaviour modification associated with HIV, compared to biological factors decreasing fecundity which could potentially be directly ameliorated by successful ART. The ideal study to evaluate this would be to analyse individual-level conception rates during periods of exposure to pregnancy for HIV positive and HIV negative women. This is not possible in survey data because sexual activity and contraceptive use are only measured at the time of the survey, not over the duration of exposure to pregnancy.
This analysis has shown that patterns of sexual exposure between HIV positive and HIV negative women by age, region and place of residence strongly mirror the patterns of relative fertility rates between the two groups. We have also shown that after adjusting for differences in exposure to recent sexual activity, young HIV positive women may have somewhat lower rates of conception and fertility than HIV negative counterparts, similar to that observed among women in older age groups.