RESUMO
BACKGROUND: Breastfeeding and 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 milk lipid and levonorgestrel content to establish baseline data for future research. METHODS: This sub-study recruited a balanced convenience sample from 259 participants enrolled in a parent randomized controlled trial comparing immediate to delayed (4-8 weeks) postpartum levonorgestrel IUD placement. All planned to breastfeed, self-selected for sub-study participation, and provided the first sample at 4-8 weeks postpartum (before IUD placement for the delayed group) and the second four weeks later. 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: We recruited 15 participants from the immediate group and 17 from the delayed group with 10 and 12, respectively, providing both early and late samples. 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 apparent effects on lipid content. These findings provide initial support for the safety of immediate postpartum levonorgestrel IUD initiation, though the study was not powered to detect noninferiority between groups. TRIAL REGISTRATION: This randomized controlled trial was registered with ClinicalTrials.gov (Registry No. NCT01990703) on November 21, 2013.