The relationship between pre-pregnancy BMI, pregnancy-related breast changes, and postpartum onset of lactogenesis II

Background: Lactogenesis-II (LII) marks the onset of copious milk secretion postpartum. High pre-pregnancy body mass index (BMI) is linked with delayed lactogenesis II (DLII) and subsequent breastfeeding challenges. Prenatal breast changes may be early phenotypic markers for delayed lactogenesis. Purpose: To examine the relationship between pre-pregnancy BMI, prenatal breast changes, and postpartum onset of lactogenesis II. Methods: This is a secondary analysis of a prospective randomized trial of a breastfeeding support intervention for 250 first-time birthing parents. Participants were surveyed on observed breast changes at 13-25 and 34-36 gestational weeks and onset of LII in postpartum days at one week postpartum. Delayed lactogenesis was operationalized as ≥ 4 days postpartum. Pre-pregnancy BMI was abstracted from the health record. Relationships between BMI, prenatal breast changes, and DLII were examined with contingency tables and chi-square statistics. Bonferroni corrections were made for comparisons evaluating relationships between breast changes and BMI and between breast changes and DLII (α=.004). Results: Overall, there were few differences in self-reported breast changes during pregnancy between BMI groups. One exception was that more participants in the normal/underweight group, compared to overweight and obese participants, experienced breast growth by the second trimester (p4 days postpartum, with a dose-response effect observed between increasing pre-pregnancy BMI and higher prevalence of LII beyond 4 days postpartum. Conclusions: Delayed lactogenesis-II has been defined as ≥4 days postpartum, but these data suggest that 4 days may be typical for first-time birthing parents regardless of BMI. Obese first- time birthing parents may be less likely to experience early pregnancy breast growth and more likely to experience onset of LII past 4 days postpartum or not at all. Regardless of observable breast changes, first-time birthing parents with high BMI may need increased lactation support