Effect of predictors on incidence rate of pregnancy among reproductive age women on antiretroviral therapy at public hospitals of Jigjiga and Harar Towns, Eastern Ethiopia: a retrospective cohort study

BACKGROUND: Globally, Human Immunodeficiency Virus (HIV) is the leading cause of death in women of reproductive age and accountable for a quarter of deaths during pregnancy in sub-Saharan Africa including Ethiopia. Introduction of antiretroviral therapy to women living with HIV highly improves lifestyle and the desire to have children. A comprehensive understanding of baseline predictors of pregnancy among women receiving ART essential to reduces unintended pregnancies, appropriate care, and preventing transmission from mother to child. OBJECTIVE: To determine the effect of baseline predictors on incidence rate of pregnancy among reproductive age women on antiretroviral therapy at public hospitals of Jigjiga and Harar town, Eastern Ethiopia from February 15 to march 15, 2020. METHODS: Retrospective cohort study was conducted on randomly selected 420 HIV-infected women using data recorded from September 11, 2014, to September 10, 2019 in Jigjiga and Harar town in Eastern Ethiopia. Simple random sampling was used to select study subjects from each hospital. Data were entered to Epi data version 3.2 and exported to Stata version 14.2 for analysis. Kaplan–Meier failure, and Cox proportional hazards model were used to estimate the incidence, and to identify predictors of pregnancy respectively. Variables which were significant (P value < 0.05) in the multivariate analysis were considered independent predictors of pregnancy. RESULTS: The overall incidence rate of pregnancy was 9.1 per 100 person-years (95% CI 7.19, 11.76). Being unadvanced HIV disease stage (AHR: 2.50; 95% CI 1.46, 4.19), having less than two children (AHR: 2.93; 95% CI 1.59, 5.40), and disclosed HIV status (AHR: 2.25; 95% CI 1.34, 3.79) were independent predictors of pregnancy. CONCLUSION: The incidence rate of pregnancy among reproductive age women on ART was found to be considerable. Being unadvanced HIV disease stage, having less than two children, and disclosed HIV status were independent predictors of pregnancy. Thus, tailoring counseling have to be designed to enhance better pregnancy planning and consecutive health outcomes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12905-022-02135-9.