Mixed methods investigate the association between HIV, ART and fertility following scale-up of HIV treatment and care in South Africa. Two longitudinal analyses of surveillance data from the Africa Centre for Health and Population Studies compare factors associated with live birth by HIV and ART exposure. Semi-structured interviews with women enrolled on ART and healthcare providers explore perceptions of childbearing and contraceptive use. A quantitative study reports on one open cohort analysis and a subsequent closed cohort. Crude Birth Rates declined since 2005 and an open cohort analysis (2007-2013) found consistently lower birth-rates amongst women on-ART, compared to HIV-positive ART-naïve women and HIV negative women. One exception was found in the 25-29year age group: incidence was 38% higher to women on ART than ART-naïve women. Crude incidence of live birth was 6.6 births/100 women-years and decreased with increasing age, higher parity, poorer self-reported health, urban area of residency, knowledge of own HIV status, being single or engaged/married, not living with a partner, awareness of the benefits of ART, use of contraception and use of injectable methods. Annual likelihood (aHR, 0.39; 95% 0.347 – 0.441) was 61% lower to HIV positive versus negative women in multivariable Poisson analysis and exposure to ART was associated with 38% reduced likelihood (aHR, 0.62; 95% 0.487 – 0.799). In a subsequent closed cohort, HIV ‘unknown’ women demonstrated similar incidence and associated factors of live birth compared to HIV negative women. HIV positive women were less likely than HIV negative and HIV ‘unknown’ women to use contraception. Women described inconsistent injectable use in semi-structured interviews due to side effects and perceptions that injectables make women ‘watery’ or are unnecessary on ART. Family planning counselling was under-prioritised within the health care service and women were unaware of safer conception topics. Recent pregnancies were considered unintended and most women desired to avoid childbearing considering current family size, economic and health risks. Partner expectations could override strong concerns for health, however, and HIV positive women were at similar risk of live birth to HIV negative women when in a regular relationship or living with a partner.