Low milk production poses a substantial challenge to exclusive and continued breastfeeding, which affects 10–15% of lactating mothers. This study aimed to explore the relationships between MP and both the maternal body mass index (BMI) and changes in breast volume during pregnancy and lactation.
Lactating mothers at 1–6 months postpartum conducted 24 h MP measurements using the test weighing method (n = 316; 74—low milk production (LMP), <600 mL; 242—normal milk production (NMP), ≥600 mL). Demographic and obstetric data, including maternal age, parity, infant sex, and birth mode, as well as pre-pregnancy and postpartum body mass index (BMI) and bra size, were provided. Maternal breast volume (cm3) was calculated based on both bra cup size and band size. Descriptive statistics, Student’s t-test, two-proportion z-test, correlation analysis and multivariable linear regression models were applied to elucidate maternal factors related to milk production.
The 24 h milk production in the LMP group was 466 ± 120 mL (80–599 mL) and 850 ± 191 mL (601–1682 mL) in the NMP group (p = 0.001). No significant differences were found between the groups in pre-pregnancy BMI, postpartum BMI, and BMI change (ΔBMI), as well as pre-pregnancy and postpartum breast volume, and breast volume increase (Δ breast volume). Both pre-pregnancy and postpartum BMI were positively correlated with pre-pregnancy and postpartum breast volume (r = 0.59–0.67, p = 0.001, for all). There was a higher proportion of mothers with Δ breast volume < 200 cm3 in the LMP group compared with the NMP group (63% (41/65) vs. 45% (91/204), respectively, p = 0.020). There was no difference in milk production between the LMP groups with Δ breast volume < 200 cm3 and Δ breast volume > 200 cm3. However, mothers in the LMP group with Δ breast volume < 200 cm3 had lower milk production compared to both the NMP group with Δ breast volume < 200 cm3 (mean difference ± standard error: 379 ± 34 mL, p < 0.001) and NMP group with Δ breast volume > 200 cm3 (414 ± 33 mL, p < 0.001). Similarly, the LMP group with Δ breast volume > 200 cm3 had a lower MP compared to both the NMP group with Δ breast volume < 200 cm3 (343 ± 42 mL, p < 0.001) and NMP group with Δ breast volume > 200 cm3 (377 ± 41 mL, p < 0.001). In addition, mothers in the LMP group with Δ breast volume > 200 cm3 had a higher postpartum BMI compared to both the NMP group with Δ breast volume < 200 cm3 (mean difference 4.1 ± 1.5, p < 0.033) and NMP group with Δ breast volume > 200 cm3 (mean difference 4.6 ± 1.5, p < 0.011).
These preliminary results highlight the complex relationships between maternal BMI, increase in breast volume and 24 h milk production, and suggest that BMI and breast growth are potentially important indicators of milk production. Further investigations of these inter-related factors may inform interventions aiming at achieving normal milk production in women with higher adiposity.
Author Contributions
Conceptualization, X.J., C.T.L. and D.T.G.; methodology, C.T.L., J.L.M. and Z.G.; software, X.J. and C.T.L.; validation, X.J. and C.T.L.; formal analysis, X.J.; investigation, X.J. and C.T.L.; resources, S.L.P. and D.T.G.; data curation, X.J., C.T.L., J.L.M. and Z.G.; writing—original draft preparation, X.J.; writing—review and editing, C.T.L., S.L.P., Z.G. and D.T.G.; visualization, X.J.; supervision, C.T.L., S.L.P. and D.T.G.; project administration, D.T.G.; funding acquisition, D.T.G. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by an unrestricted research grant from Medela AG (Switzerland), by The University of Western Australia (UWA) and China Scholarship Council (CSC). C.T.L., S.L.P., J.L.M., Z.G. and D.T.G. receive salaries from an unrestricted research grant paid by Medela AG and administered by UWA. X.J. is supported by UWA—CSC Joint PhD Scholarship and UWA—CSC Higher Degree by Research Top-Up Scholarship. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
Institutional Review Board Statement
The study was conducted in accordance with the Declaration of Helsinki and was approved by the UWA Human Research Ethics Committee (2019/RA/4/20/4023).
Informed Consent Statement
Informed consent was obtained from all participants involved in the study.
Data Availability Statement
Data sharing is not applicable.
Acknowledgments
We are grateful to the families who participated in the study.
Conflicts of Interest
D.T.G. declares participation in the Scientific Advisory Board of Medela AG. C.T.L., S.L.P., J.L.M., Z.G., and D.T.G. are/were supported by an unrestricted research grant from Medela AG, administered by The University of Western Australia. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
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