Milk Production in Mothers with and without Signs of Insulin Resistance

Abstract

Maternal obesity is associated with shortened breastfeeding duration. Insulin resistance is a physiologic hallmark of obesity and may underlie lactation difficulties in obese and other insulin resistant mothers. Our objective is to compare 24‐hour milk production in mothers with signs of insulin resistance (IR) versus those without. We examined baseline data from the MALMS study, a randomized placebo‐controlled trial of metformin to augment low milk supply. Baseline eligibility includes: mother 1–8 weeks postpartum, healthy term infant that is currently requiring formula supplement to achieve sufficient growth, but mother has strong desire to improve breast milk production. Mothers fitting this description were referred to the study by area health care providers. At baseline, all women complete a weighed record of milk production over 24 hours and undergo evaluation for trial eligibility, including the following signs of IR: fasting plasma glucose ≥ 95 mg/dL, abdominal obesity, recent gestational diabetes, or polycystic ovary syndrome. We compared relative ranking of baseline 24‐hour milk production in IR versus no IR groups, and then in obese versus non‐obese groups, with the Wilcoxon test. Of 48 women who completed baseline measurements, 33 (69%) exhibited signs of IR. Mean age (±SD) of mother (31±5 years) and infant (4±2 weeks) did not differ between groups, but BMI was significantly higher in the IR group (36.9z±7.9 versus 25.4±3.6 kg/m2, P<0.001). Relative ranking of milk production was significantly lower in IR versus no‐IR: Median [interquartile range], 216[158–332] versus 377[294–598], P=0.004. Differences were less pronounced when milk output rankings were compared for obese versus non‐obese, P=0.05. While suboptimal lactation management may have contributed to low production at Baseline in some participants, our results point to an additional deficit associated with IR.Support or Funding InformationNIH 5 K12 HD051953 (PI, Tsevat, University of Cincinnati), Bridging Interdisciplinary Research Careers in Women's Health (BIRCWH award to LN‐R)