Master's Project Title:

Associations of Maternal Weight and Weight Change with Breastmilk Fat Concentration in Exclusively Breastfeeding Women

MCH Student:

Tory Bruch

Date of Defense:

August 22, 2017



Aim: Maternal adiposity has been shown to impact the macronutrient content of breastmilk, though studies are dated, small, lack information on important confounding factors, or utilize imperfect milk collection procedures and/or variable macronutrient quantification measurement techniques. My aim is to determine if maternal adiposity impacts the fat concentration of term breastmilk in early lactation.

Methods: Breastmilk samples were collected from 100 non-diabetic, nonsmoking, exclusively breastfeeding mothers at 1- and 3-months postpartum between 8:00-10:00 am as part of the Mothers and Infants Linked for Healthy Growth (MILk) Study. Breastmilk fat concentration was measured using the Calais Human Milk Analyzer, a mid-infrared spectrophotometer which we validated against the Mojonnier method. Multiple linear regression models, controlling for potential confounders including maternal, infant, and technical factors were constructed to determine the association between breastmilk fat percentage (%fat) and maternal pre-pregnancy BMI (kg/m2), postpartum weight loss (kg), third trimester oral glucose challenge test scores (mg/dL), and gestational weight gain exceeding Institute of Medicine guidelines (yes/no).

Results: Milk fat percentage was approximately 5% at both 1- and 3-months postpartum. Almost half of mothers (49%) had a normal pre-pregnancy BMI (18.50-24.99 kg/m2), 31% were overweight (25.00-29.99 kg/m2), and 20% were obese (≥30.00­ kg/m2). Subclinical glucose intolerance was more prevalent among obese mothers (p=0.04). Almost half (46%) of women had excessive gestational weight gain. Obese mothers at 3-months postpartum lost less weight than normal or overweight mothers (p=0.05). Maternal pre-pregnancy BMI had a small, positive association with fat concentration at 3-months postpartum (β=0.012, p=0.04); however, this association did not remain significant after adjusting for potential confounding factors. No other adiposity-related factors—excessive gestational weight gain, postpartum weight loss, or third trimester blood glucose levels—were associated with breastmilk fat concentration.

Conclusions: Maternal adiposity has limited impact on the fat concentration of breastmilk during the early postpartum period. However, the prevalence of excessive gestational weight gain across all BMI subcategories suggests the need for further research to explore a possible negative association between excessive gestational weight gain and breastmilk fat concentration in early lactation.