A Cochrane review included 30 studies involving a total of 13 923 participants, generating 16 comparisons between first-generation (e.g., norethisterone, norethindrone, lynestrenol), second-generation (levonorgestrel, norgestrel) and third-generation (desogestrel, gestodene, norgestimate) progestogens. A clinically relevant difference in effectiveness among the different progestogens was not observed. Generally, trials with a follow-up period of up to 1 year or longer showed a failure rate ranging from 0.2 to 1.8%. There was less discontinuation with second- compared to first-generation progestogens (RR 0.76, 95% CI 0.67 to 0.86; 3 trials, n=2709); this remained significant when only double-blind trials were considered (RR 0.79, 95% CI 0.66-0.94; n=812). There was no difference in discontinuation when monophasic COC's containing third-generation progestogens were compared with COC´s containing second-generation progestogens in double-blind trials (RR 0.79, 95% CI 0.50-1.26). Women in the third-generation group experienced less intermenstrual bleeding than the second-generation group (RR 0.71, 95% CI 0.55-0.91; 1 trial, n=456).
Comment: The quality of evidence is downgraded by limitations in study quality.