The Clinical Usefulness of Breast Milk Sodium in the Assessment of Lactogenesis

Abstract

A study was undertaken to assess the value of breast milk sodium concentration (BM [Na+]) during early lactogenesis in predicting nursing outcome. Samples of breast milk from 130 nursing mothers were obtained between the 3rd and 8th postpartum day for analysis of BM [Na+]. Approximately half the mothers were referred for nursing problems, although no problems were anticipated in the other primiparous mothers. A BM [Na+] of < or = 16 mmol/L was considered normal. For women with normal BM [Na+], follow-up was scheduled at 1 month, whereas those with high [Na+] were evaluated more frequently with repeated [Na+] determinations. Of the 65 women with normal BM [Na+] (excluding five mothers who had experienced breast surgery), 95.4% were exclusively and successfully breast-feeding at 1 month without intervention. Of 60 women with high BM [Na+], all of whom received intervention, 55% were ultimately successful. In general, those who failed tended to have higher initial [Na+] determinations; additionally, the longer the [Na+] remained elevated, the lower the success rate. Infant weight gain was greater if the initial BM [Na+] was normal. Infants of mothers with normal BM [Na+] gained an average of 994 g above birth weight by 1 month in contrast to the average weight gain of 818 g in infants of mothers with initially elevated [Na+]. This study suggests that a normal drop in [Na+] is highly predictive of successful lactation, although a prolonged elevation of [Na+] signifies impaired lactogenesis with a high risk of failure. The clinical usefulness and limitations of this determination are discussed.