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

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.