Examining Why Age-Disparate Relationships Influence Unsafe Sex Postpartum Among South African Women: Relationship Control and Physical Partner Violence as Explanatory Mechanisms.

HIV incidence rates in South Africa are extremely high, particularly postpartum. However, there is limited knowledge of women's HIV risk behavior postpartum. Women in age-disparate relationships may be less able to negotiate safe sex postpartum than women whose partners are similar ages because they have less relationship power. The study's purpose is to test whether being in an age-disparate relationship predicts postpartum unsafe sex and to explore relationship control and intimate partner violence (IPV) as explanatory mechanisms. Data are obtained from 516 HIV-negative participants who completed a survey during pregnancy and at 14 weeks postpartum as part of a longitudinal study in Durban. Age variables, relationship control, and IPV during pregnancy were included in a multivariate model predicting unsafe sex postpartum. We also assessed whether the hypothesized mediators explained the association between being in an age-disparate relationship and unsafe sex postpartum by using indirect effect analysis with bootstrapping. Women's mean age was 24.34 years (range = 18.03-45.36); the mean difference in ages in relationships was 3.19 years (range = -6.1 to 30.1). More than a quarter reported unsafe sex postpartum (27%). Age-disparate relationship, lower relationship control, and higher IPV were each longitudinally associated with unsafe sex. Relationship control, but not IPV, mediated the association between age-disparate relationship and unsafe sex (indirect effect [] = 0.01, 95% confidence interval [CI] = [0.0002, 0.0283]). Age disparity, relationship control, and IPV all contributed to unsafe sex postpartum. Interventions that reduce the formation of age-disparate relationships and increase women's relationship power in pregnancy are needed to reduce women's HIV risk in the postpartum period.