Incidence of pregnancy after initiation of antiretroviral therapy in South Africa: a retrospective clinical cohort analysis.

Background: Little is known about rates of incident pregnancy among HIV-positive women initiating highly active antiretroviral therapy (HAART).

Methods: We conducted a retrospective clinical cohort study among therapy-naïve women ages 18-45 initiating HAART between 1 April 2004 and 30 September 2009 at an adult HAART clinic in Johannesburg, South Africa. We used Poisson regression to characterize rates and rate ratios of pregnancy.

Results: We evaluated 5,996 women who experienced 727 pregnancies during 14,095 person-years at risk. The overall rate of pregnancy was 5.2 per 100 person-years (95% confidence limits [CL] 4.8, 5.5). By six years, cumulative incidence of first pregnancy was 22.9% (95% CL 20.6%, 25.4%); among women ages 18-25 at HAART initiation, cumulative incidence was 52.2% (95% CL 35.0%, 71.8%). The strongest predictor of incidence of pregnancy was age, with women 18-25 having 13.2 times the rate of pregnancy of women ages 40-45 in adjusted analysis. CD4 counts below 100 and worse adherence to HAART were associated with lower rates of incident pregnancy.

Conclusions: Women experience high rates of incident pregnancy after HAART initiation. Understanding which women are most likely to experience pregnancy will help planning and future efforts to understand the implications of pregnancy for response to HAART.