Background: Between 2010–2013, South Africa implemented WHO ‘Option A’ for prevention of mother to child transmission (PMTCT), where all HIV-infected pregnant women (from 14 weeks gestation) received zidovudine (AZT) as ARV prophylaxis and initiated CD4 testing at their first antenatal care (ANC) visit. After returning for a second visit to collect CD4 results, women with CD4 counts ≤ 350 were referred to the ART clinic and fast-tracked for initiation on lifelong ART while continuing to visit the ANC clinic every four weeks. Women with CD4 counts >350 were dispensed daily AZT prophylaxis at monthly follow up visits (every 4 weeks). The primary objective of this study was to evaluate adherence of HIV-infected pregnant women to recommended PMTCT services at and after their first antenatal care (ANC) visit. Methods: We conducted an observational cohort study from August 2012 to February 2013 at two primary health care clinics in Johannesburg, South Africa using routinely collected clinic data from first ANC visit for up to 60 days. Results: Of the 158 patients newly diagnosed with HIV at their first ANC visit, records indicated that 139 women initiated CD4 testing during their first ANC visit. 52 patients (33% of 158) did not return again to the clinic within 60 days. Of the 118 (84% of 139) women with known gestational age > 13 weeks and known Hb ≥ 8 g/dl who should have received a 4-week supply of daily AZT at first ANC visit, 81 women (69% of 118) had a record of AZT being dispensed. Among the 139 women with CD4 results, 72 (52%) were eligible for lifelong ART (CD4 count ≤350); however, only 2 initiated ART within 30 days. Conclusions: Loss to initiation of both single and triple ARV therapy, loss to follow-up, and treatment interruptions were common during ANC care for pregnant women with HIV after their first ANC visit.