2.1. Study setting and population

To address this aim, we conducted a secondary analysis using data from HIV‐infected women enrolled in the Strategies to Optimize ART Services for maternal and child health (MCH‐ART) trial and a parallel cohort of HIV‐uninfected pregnant women (HIV‐unexposed–uninfected study) conducted in Cape Town, South Africa. Details of both studies have been published previously (le Roux et al., 2019; Myer et al., 2016; Myer et al., 2018). Briefly, the two cohorts had similar inclusion and exclusion criteria, enrolling HIV‐infected pregnant women initiating ART and HIV‐uninfected pregnant women who were > 18 years of age between March 2013 and August 2015 at their first antenatal care (ANC) visit at a primary care center in Gugulethu in Cape Town. Women who were breastfeeding at their first postpartum visit, scheduled 7 days after delivery, were enrolled and followed through 12 months postpartum. Out of 1,087 mother–infant pairs screened at their first postpartum visit, 92 women (79 HIV‐infected women and 14 HIV‐uninfected women; 8% overall) were excluded due to not breastfeeding (le Roux et al., 2019).

Gugulethu is an urban community of approximately 300,000 people outside of Cape Town and is characterized by high levels of poverty and HIV (Myer et al., 2018; Strategic Development Information & GIS Department, 2013). Over 95% of women in this setting receive ANC prior to delivery (Myer et al., 2015). Provision of ART and prevention of mother‐to‐child transmission (PMTCT) services are provided at no cost as a part of routine ANC at all public sector clinics, in accordance with local guidelines. Starting in 2013, all HIV‐infected women attending ANC were eligible for lifelong ART, regardless of CD4 count of WHO clinical stage (WHO, 2013). All HIV‐infected women in the study initiated the local first‐line ART regimen of tenofovir (300 mg) + emtricitabine (200 mg)/lamivudine (300 mg) + efavirenz (600 mg), provided as a fixed‐dose combination pill taken once daily.

HIV‐uninfected and HIV‐infected women initiating ART were included in the present analysis if they met eligibility criteria, were followed through 12 months postpartum (n = 884), and had a singleton pregnancy (n = 7 excluded). Participants completed study visits at enrollment into ANC (baseline), delivery, 6 weeks, and 3, 6, 9, and 12 months postpartum.