Unintended pregnancy in users of nomegestrol acetate and 17β-oestradiol (NOMAC-E2) compared with levonorgestrel-containing combined oral contraceptives: final results from the PRO-E2 study

Objective: To assess and compare the risk of unintended pregnancy in NOMAC-E2 users with levonorgestrel-containing COC (COCLNG) users in clinical practice. Study design: In this observational study, new users(1) of NOMAC-E2 and COCLNG were recruited in Europe, Australia, and Latin America and followed for up to 2 years. Unintended pregnancy was expressed by the Pearl Index (contraceptive failures per 100 women-years [WY]), crude hazard ratios (HRcrude) and adjusted hazard ratios (HRadj). Results: Overall, 44,559 and 46,754 users were recruited to the NOMAC-E2 and COCLNG user cohorts, respectively. There were 64 unintended pregnancies in NOMAC-E2 users (0.15 per 100 WY; 95% CI, 0.11-0.19) and 200 in COCLNG users (0.41 per 100 WY; 95% CI, 0.35-0.47). The unintended pregnancy risk was statistically significantly lower in the NOMAC-E2 cohort (p<.0001) compared to the COCLNG user cohort. The HRadj of NOMAC-E2 vs COCLNG was 0.45 (95% CI, 0.34-0.60; adjusted for age, body mass index, gravidity, COC user status, education level). Conclusions: NOMAC-E2 demonstrated superior contraceptive effectiveness compared to COCLNG, likely due to the comparatively short hormone-free interval and possibly reinforced by the long half-life of NOMAC.