A retrospective cohort analysis comparing pregnancy rates among HIV-positive women using contraceptives and efavirenz- or nevirapine-based antiretroviral therapy in Kenya

BACKGROUND: Given recent concerns of efavirenz reducing the efficacy of contraceptive implants, we sought to determine if pregnancy rates differ among HIV-positive women using various contraceptive methods and efavirenz- or nevirapine-based antiretroviral therapy (ART) regimens. METHODS: We conducted a retrospective cohort analysis of HIV-positive women aged 15–45 years enrolled in HIV care facilities in western Kenya from January 2011 to December 2013. Pregnancy was diagnosed clinically and the primary exposure was a combination of contraceptive method and ART regimen. We used Poisson models, adjusting for repeated measures, as well as demographic, behavioral and clinical factors, to compare pregnancy rates among women on different contraceptive/ART combinations. FINDINGS: 24,560 women contributed 37,635 years of follow-up with 3,337 incident pregnancies. Among women using implants, adjusted pregnancy incidence for nevirapine- and efavirenz-based ART users were 1·1 (95% CI 0·72–1·5) and 3·3 (95% CI 1·8–4·8) per 100 women-years (w-y), respectively (adjusted incidence rate ratio (aIRR) 3·0, 95% CI 1·3–4·6). Among women using depomedroxyprogesterone acetate (DMPA), adjusted pregnancy incidence for nevirapine- and efavirenz-based ART users were 4·5 (95% CI 3·7–5·2) and 5·4 (95% CI 4·0–6·8) per 100 w-y, respectively (aIRR 1·2, 95% CI 0·91–1·5). Women using other contraceptive methods, except for intrauterine devices and permanent methods, experienced 3·1–4·1 higher rates of pregnancy than women using implants, with 1·6–2·8 higher rates specifically among women using efavirenz-based ART. INTERPRETATION: While HIV-positive women using implants on efavirenz-based ART faced three times higher risk of contraceptive failure than those on nevirapine-based ART, these women still experienced lower contraceptive failure rates than women on all other contraceptive methods, except for intrauterine devices and permanent methods. Guidelines for contraceptive and ART combinations should balance the failure rates for each contraceptive method and ART regimen combination against the high effectiveness of implants. FUNDING: Supported by the President’s Emergency Plan for AIDS Relief and the Centers for Disease Control and Prevention.