Background: Both breastfeeding and the use of postpartum contraception critically influence infant and maternal health outcomes. In this pilot study, we explore the effects of timing and duration of postpartum levonorgestrel exposure on breastfeeding through objective assessments of milk lipid and levonorgestrel content to establish baseline data for future research.
Methods: This substudy includes thirty-two participants from multiple clinical sites in Salt Lake City, Utah. All participants planned to breastfeed, and self-selected for this sub-study from among 259 women enrolled in a parent randomized controlled trial comparing immediate to delayed (4-8 weeks) postpartum levonorgestrel IUD insertion. Participants provided two milk samples: first at 4-8 weeks postpartum (before IUD placement for the delayed group) and second four weeks later. Participants were paired by group assignment, and we used the Wilcoxon rank sum (inter-group) and signed rank (intra-group) tests to compare milk lipid content (creamatocrit) and levonorgestrel levels between groups and time points.
Results: Fifteen participants were allocated to the immediate group and 17 to the delayed group. Initially, median levonorgestrel concentration of the immediate group (n=10) (32.5 pg/mL, IQR: 24.8, 59.4) exceeded that of the delayed group (n=12) (17.5 pg/mL, IQR: 0.0, 25.8) (p=0.01). Four weeks later, the values aligned: 26.2 pg/mL (IQR: 20.3, 37.3) vs. 28.0 pg/mL (IQR: 25.2, 40.8). Creamatocrits were similar between both groups and timepoints.
Conclusions: Immediate postpartum levonorgestrel IUD placement results in steady, low levels of levonorgestrel in milk without significant effects on lipid content. These findings support the safety of immediate postpartum levonorgestrel IUD initiation, and future research should assess time-based meaningful outcome changes to capture clinically significant differences.
Trial Registration: This randomized controlled trial was registered with ClinicalTrials.gov (registry number NCT01990703) on November 21, 2013.