Is maternal body weight or composition associated with onset of lactogenesis II, human milk production or infant consumption of mother's own milk? A systematic review and meta-analysis.

Maternal adiposity impacts lactation performance, but the pathways are unclear. We conducted a systematic review to understand whether maternal adiposity (body mass index [BMI] or % fat mass) is associated with onset of lactogenesis II (copious milk; hours), human milk production (expressed volume/24hrs), and infant consumption of mother's own milk (volume/24hrs). We used random-effects standard meta-analyses to compare the relative risk (RR) of delayed lactogenesis II (>72 hours) between mothers classified as underweight (BMI <18.5kg/m2), healthy weight (BMI 18.5-24.9 kg/m2), and overweight/obese (BMI >25kg/m2) and random-effects meta-regressions to examine associations with hours to lactogenesis II and infant milk consumption. The certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluation approach. We included 122 articles. Mothers with underweight (RR: 0.61; 95% CI: 0.46, 0.83; I2= 46.27%; 8 articles/datapoints) or healthy weight status (RR: 0.72; 95% CI: 0.61, 0.84; I2= 64.41%; 15 articles/datapoints) were less likely to experience delayed lactogenesis II than mothers with overweight/obesity. We found no association between maternal BMI and time onset of lactogenesis II (ß= 1.45 hours; 95% CI: -3.19, 6.09; p= 0.52, I2= 0.00%; 8 articles, 15 datapoints). Due to limited data, we narratively reviewed articles examining BMI or % fat mass and milk production (n=6); half reported an inverse association, and half no association. We found no association between maternal BMI (ß= 5.84mL; 95% CI: -11.92, 23.60; p= 0.51, I2= 44.18 %; 58 articles, 75 datapoints) nor % fat mass (ß= 6.54mL; 95% CI: -3.60, 16.68; p= 0.20, I2= 21.40%; 30 articles, 32 datapoints) and infant milk consumption. Certainty of evidence for all outcomes was very low. In conclusion, mothers with overweight/obesity may be at risk of delayed lactogenesis II. Available data do not support an association with infant milk consumption but included studies do not adequately represent mothers with obesity. PROSPERO REGISTRATION #: 285344 STATEMENT OF SIGNIFICANCE: While results suggest mothers with overweight/obesity may be at risk of delayed lactogenesis II, it is important to note that available data do not adequately represent mothers at the higher end of the BMI and % fat mass spectrum (BMI >30 kg/m2, % fat mass >40%). Future research should explore the association between maternal body weight or composition and lactation outcomes including onset of lactogenesis II, human milk production and infant consumption of mother's own milk among mothers with greater variability in weight status. Understanding these relationships may help guide the creation of more specialized lactation care for mothers of all body sizes.