(P10-074-24) Maternal Milk Production Rate at 2 and 6 Weeks Postpartum

Objectives: Objective measures of maternal milk production capacity are lacking, limiting elucidation of maternal contributors to under- and over-production of breast milk. Here, we describe hourly milk production at 2 and 6 weeks postpartum among women with exclusive breastfeeding (EBF) intention in relation to EBF achievement and obesity status.

Methods: MOM2CHild is a prospective study enrolling expectant mothers through April 2024 who indicate strong EBF intention. Study visits at 2 and 6 weeks postpartum include assessing infant weight and EBF status; and complete breast expressions at hours (h) 0, 1, and 2. Milk production rate (MPR, g/h) is defined as milk yield at h2, based on prior validation of steady state reached at h2. EBF status is grouped as: 1. EBF with no infant weight gain concerns, 2. EBF with weight gain concerns, 3. striving for EBF with supplement use, and 4. elective supplement use. BMI is based on self-reported pre-pregnancy weight and height, with obesity defined as BMI ≥35.0 kg/m². Kruskal Wallis, ANOVA, t-tests and chi-square were used to compare MPR across groups.

Results: MPR results are available for n=65 at week 2, and n=61 at week 6. Most participants are privately insured (88%) with some college (84%). Racial distribution is 19% Black, 75% White, and 6% other. Mean (SD) pre-pregnancy BMI is 27.2 (6.6) kg/m2. Median [q1-q3] grams milk expressed declined across h0-h2 at both weeks 2 and 6 (e.g., week 2, h0: 112 [54-156], h1: 65 [44-93], h2: 41 [31-53]; p < 0.00001), but h2 MPR did not change significantly between weeks 2 to 6 (n=53, 44±20 vs. 48±18 g/h; paired t-test p=0.18). MPR varied by EBF status at both week 2 (group 1: n=50, 49±17; group 2: n=6, 31±16; group 3: n=6, 21±13; group 4: n=3, 33±27; p=0.00003) and week 6 (group 1: n=45, 51±16; group 2: n=6, 40±11; group 3: n=6, 22±11; group 4: n=4, 39±15; p=0.00002), though breast emptying frequency did not vary by EBF status at week 2 (p=0.38) or week 6 (p=0.43). MPR in the at-risk range (≤35 g/h) was 2.1-fold higher in women with obesity versus without obesity (e.g., week 2 prevalence: 59% (10/17) vs. 28% (13/46), respectively, p=0.025).

Conclusions: Hourly MPR results suggest that milk production is stabilized by two weeks postpartum and reflects EBF and obesity status. Future research will model clinical and biochemical predictors of MPR.

Funding Sources: NICHD, NIAID