Table 3.
Pregnancy incidence per 100 women-years for each contraceptive method and antiretroviral therapy (ART) regimen
| Variable | Unadjusted pregnancy rate§ per 100 women-years (95% CI) | Adjusted pregnancy rate# per 100 women- years (95% CI) | Adjusted pregnancy rate ratios# per 100 women-years (95% CI) (model without an interaction term) | Adjusted pregnancy rate ratios¶ per 100 women-years (95% CI) (model with an interaction term) |
|---|---|---|---|---|
| Contraceptive method | ||||
| Implant | 3.0 (2.3–3.6) | 1.4 (1.1–1.8) | Ref. | Ref. |
| Depomedroxyprogesterone acetate (DMPA) | 8.9 (8.2–9.6) | 4.3 (3.7–4.9) | 3.1 (2.4–3.8) | 1.6 (0.83–2.5) |
| Combined oral contraceptives or oral contraceptive pills (COCs or OCPs) | 11.7 (9.4–14.1) | 5.8 (4.5–7.2) | 4.1 (2.9–5.4) | 2.8 (0.97–4.7) |
| Other more effective contraception (IUDs, permanent) | 1.3 (0.69–1.9) | 1.1 (0.56–1.6) | 0.78 (0.37–1.2) | 0.29 (0–0.71) |
| Less effective contraception (condoms, “natural” methods) | 13.1 (12.5–13.7) | 5.6 (4.6–6.6) | 4.0 (3.0–4.9) | 1.6 (0.86–2.4) |
| No contraceptive method | 7.4 (6.8–7.9) | 4.8 (3.9–5.8) | 3.4 (2.6–4.3) | 1.2 (0.62–1.8) |
| Antiretroviral therapy (ART) regimen | ||||
| Nevirapine-based ART | 8.8 (8.3–9.2) | 4.4 (3.8–5.1) | Ref. | Ref. |
| Efavirenz-based ART | 7.5 (6.8–8.2) | 4.5 (3.7–5.3) | 1.0 (0.90–1.1) | 3.0 (1.3–4.6) |
| Lopinavir/ritonavir-based ART | 8.4 (6.9–9.9) | 5.0 (3.8–6.1) | 1.1 (0.91–1.3) | 0.86 (0–2.1) |
| No ART | 11.8 (11.1–12.5) | 4.3 (3.6–5.0) | 0.97 (0.89–1.1) | 1.2 (0.60–1.8) |
Calculated with an unadjusted Poisson model that included ART regimen for contraceptive method and contraceptive method for ART regimen (but not an interaction term).
Calculated with an adjusted Poisson model that included contraceptive method and ART regimen (but not an interaction term between contraceptive method and ART regimen) and covariates adjusted for included age, educational attainment, marital status, number of living children, HIV-positive status disclosure to partner, and time-dependent covariates of percent use of condoms, body mass index (BMI), World Health Organization (WHO) stage, CD4 cell count, and use of anti-tuberculosis medications during the observation period.
Calculated with an adjusted Poisson model that included an interaction term between contraceptive method and ART regimen and covariates adjusted for included age, educational attainment, marital status, number of living children, HIV-positive status disclosure to partner, and time-dependent covariates of percent use of condoms, body mass index (BMI), World Health Organization (WHO) stage, CD4 cell count, and use of anti-tuberculosis medications during the observation period. The reference group for ART regimen is efavirenz-based ART when generating the rate ratios for the contraceptive methods. The reference group for contraceptive method is implants when generating the rate ratios for the ART regimens.