Objective: To investigate the dynamics of milk removal during breast expression.
Subjects and methods: This study used a continuous weighing balance to determine changes in milk flow rate and their relationship to the proportion of milk removed over time and the percentage of the available milk removed during simultaneous expression (15 minutes) of the left and right breasts in 34 mothers of healthy, term, breastfeeding infants.
Results: Multiple milk ejections (5.1±2.0; range, two to 14) were detected as increases in milk flow rate. A larger total expression volume was associated with a higher maximum milk flow rate (p<0.001). However, 14% less of the available milk was removed for a 100 g increase in available milk (p<0.001). After 2.9±1.4 and 6.0±2.5 minutes, 50% and 80%, respectively, of the total expression volume was removed. Milk flow was more active in the first 7 minutes than the last 7 minutes. At the eighth minute (midpoint), 54±25% of the available milk and 86±9% of the total expression volume were removed.
Conclusions: The maximum milk flow rate was predictive of the total volume expressed. After the eighth minute of expression the milk flow rate was reduced. Increasing volumes of milk in the breast were associated with less complete breast emptying. These data suggest that long expression sessions are not required for mothers who are not pump dependent and that extending intervals between expressions results in less effective milk removal.