Unintended pregnancy rates differ according to combined oral contraceptive - results from the INAS-SCORE study

Objectives: To estimate the real-use contraceptive effectiveness of the combined oral contraceptive (COC) containing dienogest and oestradiol valerate (DNG/oEV) compared to other combined oral contraceptives (oCOC) and particularly, levonorgestrel-containing OCs (LNG). Methods: Prospective, non-interventional cohort study with two main exposure groups and one exposure subgroup: new users of DNG/oEV and oCOC, with the subgroup, LNG. In a planned secondary analysis, pregnancy outcomes were investigated, including contraceptive failure. The influence of age, parity and OC-type were assessed. Results: 30,098 COC users were followed for a total oral contraceptive exposure time of 68,362 woman-years (WY) and 287 unintended pregnancies were reported. The overall contraceptive failure rate in the European population was 0.4 events/100 WY (95% CI, 0.4-0.5). DNG/oEV showed lower contraceptive failure rates compared to the comparators. This difference was maintained when the study population was restricted to women aged 18-35 years; the pearl index (PI) for this demographic for DNG/oEV was 0.37 (95% CI 0.24-0.54) and 0.76 (95% CI 0.56-1.01) for LNG. The hazard ratios (HRs) adjusted for age, parity, smoking and BMI were 0.7 (95% CI, 0.5-0.98, p = .04) and 0.5 (95% CI, 0.3-0.8, p < .01) for DNG/oEV versus oCOC and LNG, respectively. The corresponding adjusted HRs in women aged 25 years or younger were 0.6 (95% CI 0.4-1.1) and 0.4 (95% CI, 0.2-0.8), respectively. Conclusions/discussion: DNG/oEV showed improved contraceptive effectiveness compared with oCOC and particularly LNG-COC when adjusted for age, parity, user status and smoking.