Effectiveness and efficacy rates of progestin-only pills: A comprehensive literature review.

OBJECTIVES: To synthesize published literature on POP effectiveness and efficacy.

STUDY DESIGN: We searched PubMed Central, PubMed, and the Cochrane library through March 07, 2022. We included articles written in English reporting a Pearl Index or life table rate for pregnancy. We excluded articles only assessing formulations that: were never marketed globally, are only sold in combination with estrogen, are currently sold only for noncontraceptive purposes, or were not given to participants continuously. Four researchers independently extracted data and two analyzed data using Excel and R.

RESULTS: We included 54 studies. Among studies at low or moderate risk of bias, the median Pearl Index rate (the failure rate during typical use) was 1.63 (range 0.00-14.20, IQR 4.03) and the median method failure Pearl Index rate (the failure rate during perfect use) was 0.97 (range 0.40-6.50, IQR 0.68). Excluding the newer formulations, Desogestrel and Drospirenone, which are closer to combined oral contraceptives in that they prevent pregnancy by inhibiting ovulation, the median Pearl Index rate is 2.00 (range 0.00-14.12, IQR 2.5) and the median method failure Pearl Index rate is 1.05 (range 0.00-10.90, IQR 1.38).

CONCLUSIONS: Among studies at low or moderate risk of bias, the median Pearl Index rate during typical POP use was much lower than currently estimated (7.00), while the median perfect use rate was similar to current estimates.

IMPLICATIONS: Future research should investigate the possibility that POPs may be much more effective during typical use than currently believed.