Measuring milk synthesis in breastfeeding mothers

Breastfeeding mothers expressed their breasts hourly for periods up to 7 hours, without exogenous oxytocin, to determine the consistency of milk removal and the relationship between the volume of milk removed and the mother's 24-hour milk production.

Mothers (n = 20) measured their 24-hour milk production from each breast by test-weighing their babies at home. Mothers came to the research laboratory for a day visit and expressed milk from either both or one breast (left or right) for 10-15 minutes, every hour for 2-7 hours. Mothers were not instructed to restrict breastfeeding prior to the first (0-hour) expression.

It was found that the milk volume at 1 hour (59.7 +/- 36.5 and 46.5 +/- 25.6 mL/hour for the right and left breast, respectively) was significantly (p < 0.05) higher than the milk volume from subsequent hourly intervals. The average hourly volumes obtained from the 2nd to 7th hour (18.0 +/- 3.1 and 14.0 +/- 4.8 mL/hour for the right and left breast, respectively) were not significantly different from the average hourly rates calculated for the 24-hour milk production (18.4 +/- 6.3 and 15.5 +/- 5.1 mL/hour for the right and left breast, respectively). Furthermore, local inhibition was not observed during hourly expressions of up to 7 hours.

The average hourly volumes of milk from the 2nd to 7th hour expressions could provide an estimate of the rate of milk secretion. Further study is required to fully validate these findings.