OBJECTIVE: To assess serial secretory activation biomarker concentrations (sodium [Na], potassium [K], Na:K, protein, lactose, and citrate) in mother's own milk (MOM) from breast pump-dependent mothers of preterm infants to determine associations with coming to volume (CTV), defined as producing at least 500 mL/day MOM by day 14 postpartum.
STUDY DESIGN: We collected serial MOM samples and pumped MOM volume data for 14 days postpartum in mothers who delivered at <33 weeks of gestation. Regression models and the Mann-Whitney U test were used to evaluate associations.
RESULTS: Among 40 mothers, 39 (mean gestational age, 28.8 weeks; 67% overweight/obese; 59% nonwhite) had paired MOM volume and biomarker data; 33% achieved CTV between postpartum days 6 and 14. In univariate models, MOM Na on postpartum day 5 and Na:K on days 3 and 5 were associated with CTV. Mothers achieving CTV were more likely to have postpartum Na:K ≤1 on day 3 (75% vs 25%; P = .06) and ≤0.8 on day 5 (69% vs 10%; P < .01). In a multivariable regression model, day 5 Na:K (1 unit decrease in Na:K: OR, 18.7; 95% CI, 1.13-311.41; P = .049) and maternal prepregnancy body mass index (BMI) (1 unit increase in BMI: OR, 0.88; 95% CI, 0.78-0.99; P = .04) were associated with CTV between postpartum days 6 and 14.
CONCLUSIONS: Secretory activation and CTV were compromised in breast pump-dependent mothers with preterm delivery. CTV was predicted by MOM Na level and Na:K. These biomarkers have potential as objective point-of-care measures to detect potentially modifiable lactation problems in a high-risk population.