When can a woman have repeat progestogen-only injectables–depot medroxyprogesterone acetate or norethisterone enantate?

Background Currently, there is a generally accepted 2-week grace period for women returning early/late for reinjection of either depot medroxyprogesterone acetate (DMPA) or norethisterone enantate (NET-EN). This systematic review evaluates the evidence regarding return to fertility and ovulation after injection of a progestogen-only contraceptive. Study Design We searched the PubMed database to identify all relevant evidence published in peer-reviewed journals from database inception through November 2008 regarding timing of fertility and return to ovulation after the last injection of DMPA or NET-EN. Results We identified 20 articles, 10 on DMPA use, eight on NET-EN use and two examining both types of injectables. Six studies examining time to pregnancy after discontinuing DMPA or NET-EN reported that pregnancy rates during the currently recommended 2-week grace period were zero or very low. Studies of return to ovulation indicated a wide variation in time to ovulation post-injection with the majority ranging from 15–49 weeks from the last injection (for DMPA) and 4.9–24.3 weeks from the last injection (for NET-EN). Limitations of this body of evidence include small sample sizes, lack of data on the main outcome of interest (time to pregnancy) and inconsistency in measurement of ovulation, a surrogate measurement for pregnancy risk. Conclusion Studies evaluating time to pregnancy after last injection of DMPA or NET-EN reported extremely low pregnancy rates during the 2-week interval following the reinjection date; extremely low pregnancy rates for DMPA were also reported for 4 weeks following the reinjection date. Studies of return to ovulation after last injection of DMPA generally found that the earliest ovulation did not occur until several months after the last injection while studies of NET-EN reported ovulations around (or even before) the time for reinjection.