Breastfeeding patterns among parturients with diabetes: a secondary analysis of the MOMPOD randomized clinical trial.

Introduction: Insulin resistance is associated with decreased milk supply in lactating people. Metformin is hypothesized to increase breast milk production by decreasing insulin resistance, suggesting use may increase breastfeeding success. We aimed to determine the association between metformin use during pregnancy and breastfeeding initiation and continuation.

Methods: This was a secondary analysis of the MOMPOD randomized controlled trial of metformin versus placebo in addition to insulin therapy among pregnant people with type 2 diabetes and early diabetes. We included parturients who delivered a living neonate, received at least one dose of study drug or placebo, endorsed an intention to breastfeed, and completed a breastfeeding survey. Breastfeeding intentions and breastfeeding outcomes were collected utilizing a breastfeeding questionnaire at 24-30 weeks and 30-days postpartum respectively. The primary outcome was breastfeeding at 30-days postpartum defined by exclusive or partial breastfeeding. Secondary outcomes included immediate breastfeeding defined as any breastfeeding during the postpartum hospital admission until at least postpartum day 3, onset of lactogenesis (days), breast and bra size, and breastfeeding challenges. Baseline characteristics and outcomes were compared using chi-square, t-test, or Wilcoxon tests, as appropriate.

Results: Among the 794 women randomized and receiving either placebo or metformin in the primary trial, 378 (47.6%) met inclusion criteria with 194 (51.3%) in metformin and 184 (48.7%) in placebo groups. There were no significant differences in baseline characteristics. Immediate breastfeeding was comparable between groups (91.1% vs 88.9%, p=0.53) and there was no difference in onset of lactogenesis. Thirty days postpartum, breastfeeding rates were lower among all parturients and there was no difference between metformin and placebo groups (76.0% vs 66.7%, p=0.11). Also, there were no differences in partial or exclusive breastfeeding, breast cup or bra size, or breastfeeding challenges.

Conclusion: Our data suggest no association between metformin use and breastfeeding patterns in those with type 2 or early diabetes in pregnancy. Antepartum metformin should not be recommended solely to improve breastfeeding success.