HIV acquisition in pregnancy: implications for mother-to-child transmission at the population level in sub-Saharan Africa

Abstract

Introduction: A recent sero-discordant couple study showed an elevated risk of HIV-acquisition during the pregnancy/postpartum period per-condomless-coital-act. This, along with previous studies, has led to concern over possible increased risk of mother-to-child (vertical) transmission, due to the initial high viral load in the first months after seroconversion, in a time when the woman and health services may be unaware of her status. This study looks at whether behavioural differences during the pregnant/postpartum period could reduce the impact of elevated risk of HIV acquisition per-condomless-coital-act at the population level.

Methods: We used data from 60 demographic and health surveys from 32 sub-Saharan African countries. Using the HIV status of couples, we estimated differences in serodiscordancy between HIV-negative women who were pregnant/postpartum compared to those who were not pregnant/postpartum. We compare the risk of sexual activity over the pregnant/postpartum period to those not pregnant/postpartum. Using these risks of serodiscordancy and sexual activity along with estimates of increased HIV risk in the pregnancy/postpartum period per-condomless-coital-act, we estimated a population-level risk of HIV acquisition and acute infection, during pregnancy/postpartum compared to those not pregnant/postpartum.

Results: Sexual activity during pregnancy/postpartum varies considerably. In general, sexual activity is high in the first trimester of pregnancy, then declines to levels lower than among women not pregnant/postpartum, and is at its lowest in the first months postpartum. Adjusted for age and survey, pooled results show HIV-negative pregnant women are less likely to have an HIV-positive partner compared to those not pregnant/postpartum (risk ratio (RR) = 0.78, 95% CI = 0.68-0.89) and comparing the postpartum period (RR = 0.85, 95% CI = 0.73-0.99). Estimated population-level risk for HIV acquisition and acute infection in pregnancy/postpartum was lower than would be inferred directly from per-condomless-coital-act estimates in most countries, over the time of most risk of mother-to-child transmission, though there was variation by country and month of pregnancy/postpartum.

Conclusions: Estimates of population-level HIV acquisition risk in sub-Saharan Africa should not be taken directly from per-condomless-coital-act studies to estimate vertical transmission. Changes in sexual behaviour and differences in HIV-serodiscordancy during pregnancy/postpartum reduce the impact of increased risk of HIV acquisition per-condomless-coital-act, this will vary by region.

Keywords: HIV; HIV acquisition; paediatric; postpartum; pregnancy; vertical transmission.

Figure 1

Risk ratios of sexual activity in the last week during the pregnant and postpartum period compared to not pregnant/postpartum, HIV‐negative women, aged 15–49, adjusted for 5‐year age group and calendar year for 29 countries.

Figure 2

Typical patterns of risk ratios of sexual activity in the last week during the pregnant/postpartum period compared to not pregnant/postpartum, adjusted for 5‐year age group and year of survey in sub‐Saharan Africa. The shaded area is the postpartum period.

Figure 3

Two atypical patterns of risk ratios of sexual activity in the last week, during the pregnant/postpartum period compared to not pregnant/postpartum, adjusted for 5‐year age group and year of survey, in sub‐Saharan Africa (for Rwanda and Burundi). The shaded area is the postpartum period.

Figure 4

Estimated monthly risk ratios for HIV acquisition per‐condomless‐coital‐act from Thomson et al. [1].

Figure 5

The variation in estimated monthly population risk of HIV acquisition in pregnancy/postpartum compared with not pregnant/postpartum, using per‐condomless‐coital‐act risk probabilities from Thomson et al. and taking into account differences in sexual activity and serodiscordance between the groups, adjusted for 5‐year age group. The red line represents the point estimates for per‐condomless‐coital‐act risk ratio at each stage of pregnancy/postpartum compared to not pregnant/postpartum from Thomson et al [1].

Figure 6

Population‐level risk ratios of HIV acquisition, comparing stages of pregnancy/postpartum to not pregnant/postpartum women, for selected countries. Point estimates using risk ratios per‐condomless‐coital‐act using gradients of risk ratios per‐condomless‐coital‐act and lighter lines the 95% confidence intervals in green. The grey line represents the risk ratio per‐condomless‐coital‐act from Thomson et al [1]. Also, the grey shading is for the months postpartum.

Figure 7

Estimated ratio of acute infections in the ninth month of pregnancy (top) and the third month postpartum (pp) (bottom), compared to not pregnant/postpartum women, assuming no ART initiation. Estimates use per‐condomless‐coital‐act probability taking into account differences in sexual activity in the last week and HIV‐serodiscordancy with a partner, assuming an acute infection window of 3 months. Shown for each country given their sexual activity patterns (blue). Confidence intervals represent uncertainty around the per‐condomless‐coital‐act risk ratio estimates. Also plotted is the point estimate of the per‐condomless‐coital‐act risk ratios from Thomson et al [1] (red).