Milk flow rates can be used to identify and investigate milk ejection in women expressing breast milk using an electric breast pump.

Currently there is no simple method available to assess milk ejection and breast milk flow in lactating women in both the clinical and research setting. The authors hypothesize that changes in milk flow rate are associated with milk ejection and therefore may provide a method suitable for the assessment of milk ejection and removal. Mothers (n = 23) expressed milk from one breast for a 15-minute period using both weak and strong vacuums on two to four separate occasions using an experimental electric breast pump (Medela AG, Baar, Switzerland). Breast milk flow rates were recorded at 5-second intervals by connecting a tube from the breast shield to a bottle placed on a balance that was connected to a computer. Milk ejection was determined by an acute increase in milk duct diameter in the contralateral breast using ultrasound (Acuson XP10, Siemens, Mountain View, CA), and the change in duct diameter was compared with milk flow rates. Milk flow rates ranged from 0 to 4.6 g per 5-second period. Increases in flow rates were positively associated with increases in duct diameter (p < 0.05). Furthermore, within each milk ejection, higher maximum duct diameters were positively related to greater volumes expressed per 5-second periods (p < 0.001). Time to the first milk ejection and number of milk ejections were the same when determined by ultrasound or flow rates. This direct relationship between increases in duct diameter and acute increases in milk flow rates suggests that changes in flow rates can be used to identify milk ejection in the absence of ultrasound data.