Objective: HIV-positive pregnant women are at heightened risk of becoming lost to follow-up (LTFU) from HIV care. We examined LTFU before and after delivery among pregnant women newly-diagnosed with HIV. Methods: Observational cohort study of all pregnant women ≥18 years (N=300) testing HIV-positive for the first time at their first ANC visit between January–June 2010, at a primary healthcare clinic in Johannesburg, South Africa. Women (n=27) whose delivery date could not be determined were excluded. Results: Median (IQR) gestation at HIV testing was 26 weeks (21–30). 98.0% received AZT prophylaxis, usually started at the first ANC visit. Of 139 (51.3%) patients who were ART-eligible, 66.9% (95%CI 58.8–74.3%) initiated ART prior to delivery; median (IQR) ART duration pre-delivery was 9.5 weeks (5.1–14.2). Among ART-eligible patients, 40.5% (32.3–49.0%) were cumulatively retained through six months on ART. Of those ART-ineligible at HIV testing, only 22.6% (95%CI 15.9–30.6%) completed CD4 staging and returned for a repeat CD4 test after delivery. LTFU (≥1 month late for last scheduled visit) before delivery was 20.5% (95%CI 16.0–25.6%) and, among those still in care, 47.9% (95%CI 41.2–54.6%) within six months after delivery. Overall, 57.5% (95%CI 51.6–63.3%) were lost between HIV testing and six months post-delivery. Conclusions: Our findings highlight the challenge of continuity of care among HIV-positive pregnant women attending antenatal services, particularly those ineligible for ART.