(PTFS09-05-26) Longitudinal Evaluation of Secretory Activation, Milk Composition, and Infant Growth in the First Month Postpartum

Sunday, July 26, 2026

2:46 PM - 2:50 PM ET

Location: Prince George's Hall B-E (The Hub) - Poster Theater 1 / Poster Board Number: PT1-5

Presenting Author(s)

Leigh A. Martin, PhD (she/her/hers)

Postdoctoral Associate
Cornell University
Ithaca, New York, United States

Disclosure(s): No relevant financial relationship(s) with ineligible companies to disclose.

Co-Author(s)

IV

Izzy Vix

Cornell University, New York, United States
FF

Fathia Farah

Cornell University, New York, United States
DC

Debbie Chen

Cornell University, New York, United States
ZL

Zhengfei Li

Cornell University, New York, United States
NF

Nicole G. Fischbein

University of California San Francisco
San Francisco, California, United States
FJ

Flora G. Jin

University of California San Francisco
San Francisco, California, United States
NA

Nadav G. Ahituv

University of California San Francisco
San Francisco, California, United States
VF

Valerie Flaherman, MD, MPH

Associate Professor of Pediatrics and Epidemiology and Biostatistics
University of California San Francisco
San Francisco, California, United States
Yarden Golan Maor, PhD (she/her/hers)

Assistant Professor
Cornell University
Ithaca, New York, United States

Disclosure(s):

Leigh A. Martin, PhD: No relevant financial relationship(s) with ineligible companies to disclose.

Yarden Golan Maor, PhD: OnlyOther, Inc: Advisory Committee/Board Member (Ongoing)

Objectives: Secretory activation (SA), indicated by milk sodium and conductivity, typically occurs 2-4 days postpartum. The MyLee at‑home breast milk sensor uses conductivity within a proprietary algorithm to estimate milk maturation. Although delayed SA is linked to poorer breastfeeding outcomes, its relationship with early milk composition and infant growth over the first month remains unclear.

Methods: In a longitudinal observational cohort, we enrolled 88 lactating parent-infant dyads in California (2022–2023). Eligible dyads had singleton, full‑term infants (≥37 weeks). Participants completed surveys at enrollment and days 7, 14, 21, and 30 to report demographics, breastfeeding practices, and infant intake. Milk samples collected on days 7-30 were analyzed for milk maturation (MyLee sensor), sodium and conductivity (Horiba electrodes), and macronutrient composition (SpectraStar XT‑R). Infant weights were abstracted from medical records. Linear and mixed‑effects models assessed associations among milk maturation biomarkers, macronutrients, perceived milk production, and infant weight-for-age (WAZ).

Results: Participants were 35.9 ± 3.8 years old with mean pre-pregnancy BMI 22.9 ± 3.4 kg/m². Mean milk maturation scores were 86.9 ± 8.1%, 94.6 ± 5.5%, 96.5 ± 4.5%, and 99.1 ± 4.4% on days 7, 14, 21, and 30, respectively; they were significantly correlated with mean sodium concentration on all days (all r=-0.7, p< 0.01). Mean protein concentration was 1.73 ± 0.18 and 1.52 ± 0.14 on days 14 and 30, respectively (p < 0.0001). There was no significant difference in carbohydrate or fat concentrations. Mean protein concentration was significantly related to WAZ at day 14 (β = -1.47, p < 0.05). There were no significant relationships between SA biomarkers and WAZ. Dyads reporting oversupply had infants with higher WAZ (+0.67) and higher milk conductivity (+0.32), while dyads reporting undersupply had infants with lower WAZ (−0.59), relative to sufficient supply (p < 0.05).

Conclusions: In this breastfeeding cohort, SA biomarkers were not significantly related to infant WAZ over 1 month postpartum. There were significant relationships between protein concentration, perceived milk production, and WAZ, suggesting a biological link between perceived milk production and breastfeeding outcomes.

Funding Sources: NICHD (1K99HD113880-01A1) and Mount Zion Health Fund