Potential effect of immediate postpartum use of injectable contraception on lactogenesis

We evaluated the effect of immediate postpartum use of depot medroxyprogesterone acetate (DMPA) on the timing of lactogenesis stage II (LS-II).

The initial design randomly assigned adults who delivered a full-term infant in 2019-2021 to receive within 48 hours of delivery: (1) DMPA, (2) placebo injection, or (3) no injection. Due to low enrollment, we changed in 2021-2023 to a nonrandomized design using matching at recruitment for obesity and delivery method and propensity score weighting for analysis. We combined data from both designs to compare immediate postpartum DMPA use (N = 55) vs control (placebo or no injection) group (N = 95). We defined noninferiority a priori as being met if the upper bound of a two-sided 95% CI for mean difference in time to LS-II between groups was <6 hours.

The unweighted mean time to LS-II was 57.8 hours in the DMPA group (SD, 29.4) and 64.1 hours in the control group (SD, 36.1). Using propensity score weighting to make the groups comparable with respect to age, race, delivery method, and previous live births, the mean time to LS-II was 5.5 hours shorter (95% CI, -16.4, 5.5) for women in the DMPA relative to control group.

We found no evidence that DMPA use inhibits the onset of LS-II. Findings support immediate postpartum DMPA initiation among those intending to engage in human milk feeding.

A controlled trial (N = 150) did not detect any difference in time to lactogenesis stage II ("milk let-down") between injectable contraception use within the first 48 hours postpartum and those without this exposure.