Maternal Complications of Pregnancy and Achievement of Secretory Activation and Coming to Volume in Breast Pump-Dependent Mothers of Preterm Infants

<b><i>Objective:</i></b> Mother's own milk (MOM) sodium (Na) is an objective measure of secretory activation (SA), which is often delayed or impaired after preterm delivery. We sought to determine in pump-dependent mothers of preterm infants, impacts of maternal comorbidities on lactation outcomes using objective measures, including MOM Na, pumping frequency and MOM volumes for the first 14 postpartum days. <b><i>Study Design:</i></b> In this secondary analysis of four prospective cohorts, we examined outcomes using logistic and linear regression, survival analysis, and mediation and moderation sub-analyses. <b><i>Results:</i></b> A total of 143 mothers (57.3% Black, 30.8% Hispanic; 35.0% with hypertensive disorders of pregnancy [HDP]; 9.8% diabetic; 73.8% high body mass index [BMI]) delivered at 29.1 ± 2.8 weeks. Mothers pumped 4.7 ± 1.8 times/daily. Daily pumping frequency was a significant independent predictor of all modeled outcomes (<i>p</i> < 0.001 SA achievement, maintenance, and time to SA achievement; daily MOM volume; coming to volume [CTV; 500 mL/day]). 88.1% achieved SA by MOM Na ≤16 mM at postpartum day 5.6 ± 2.5. Only 41.3% of this subset continuously maintained SA until postpartum day 14. HDP was negatively associated with time to SA (<i>p</i> = 0.039). BMI values were negatively associated with MOM volume (<i>p</i> = 0.017) and CTV achievement (<i>p</i> = 0.02). Effects of daily pumping frequency were moderated by BMI (SA achievement and time to SA) and diabetes (CTV), with worse outcomes for higher BMI or diabetes despite similar pumping frequencies. <b><i>Conclusion:</i></b> Daily pumping frequency was the significant independent predictor for early lactation outcomes in a breast pump-dependent cohort of mothers of preterm infants. Further research on the interplay between modifiable and unmodifiable lactation risks in high-risk populations is needed.