Breast-milk sodium as a predictor of breastfeeding patterns.

This study partially replicates and extends a study reporting that elevated breast-milk sodium BM [Na+] during early lactogenesis was predictive of poor breastfeeding outcomes. The present study used 6-day postpartum breast milk. Consistent with the findings of the earlier study, 80% of those with a BM [Na+] of 16 mmol/L or lower at day 6 sustained a high level of breastfeeding at week 4, compared to only 50% of those with an elevated BM [Na+] (chi 2 = 4.05, df = 1, p = .04). This difference was even greater in a subgroup of mothers predicted to be at high risk for insufficient milk supply on the basis of support density and self-perception variables. Of the latter group, 75% with low BM [Na+] sustained a high level of breastfeeding at 4 weeks postpartum, compared to only 22% with an elevated BM [Na+] (chi 2 = .65, df = 1, p = .01). In contrast, among the low-risk mothers BM [Na+] levels were not associated with any difference in breast-milk sustainment (89% and 82% sustainment for low- and high-sodium groups, respectively). Thus a normal drop in BM [Na+] is predictive of higher sustainment of breastfeeding. However, the predictive validity of this marker appears to be enhanced by combining it with the psychosocial variables of support density and self-perception of breastfeeding by the mother.