Milk Ejections and Milk Flow Patterns During Breast Expression: When to Stop Pumping ^†

Despite the available evidence, mothers often do not tailor the duration of their pumping sessions to their individual milk flow pattern. Therefore, many mothers miss the opportunity to save time whilst effectively pumping their milk and maintaining their milk supply. This is particularly important for mothers that are pump-dependent, such as after preterm birth, when they need to pump 6–8 times per day. Milk ejection (ME) patterns are consistent within mothers, so while most mothers have several MEs earlier in the pumping session, others may have continuous milk flow [1]. However, milk flow patterns and the time of active milk removal during a pumping session have not been extensively characterized. We aimed to describe MEs, milk flow and milk removal patterns as well as the efficacy of milk removal and comfort during a standard Symphony (Medela AG, Baar, Switzerland) session. We also described the effects of breast fullness and late MEs on milk removal parameters.

Lactating mothers 3.8 ± 1.4 months postpartum (n = 147) participated in one to three standard Symphony sessions (n = 225) using a standard fitted shield and maximum comfortable vacuum (MCV). Mothers completed a 24 h milk production profile to allow for the calculation of the pre- and post-expression degree of fullness of the breast (DOF) and the percentage of available milk removed (PAMR). We used a continuous weighing balance to determine changes in milk flow rate [2]. The two predominant milk flow patterns during pumping were as follows: a few defined MEs (Pattern 1, ≤4 MEs) and many defined MEs (Pattern 2, ≥5 MEs). Sessions with late MEs (MEs that occurred ≥ 3 min after milk flow stopped) were also investigated. Linear mixed effect models were used to evaluate the effects of milk flow patterns on the efficacy of milk removal and other relationships between milk removal parameters. When two Symphony sessions (n = 76) were completed by the same participant, DOF pre-expression was categorized as ‘emptier’ or ‘fuller’, and paired t-tests were conducted to compare the two sessions. Mothers completed a single pumping session (n = 71), two sessions (n = 74) or three sessions (n = 2). Overall, the average amount of milk removed, PAMR and number of MEs was 76 ± 49 g, 66 ± 26% and 4.5 ± 1.6, respectively. Milk flow patterns were consistent within mothers, and the two patterns were equally represented between mothers: Pattern 1: single sessions (55%), double (51%); Pattern 2: single sessions (45%), double (27%).

Degree of fullness: A higher pre-expression DOF was observed with Pattern 2 (0.49 (0.14), p < 0.001) and a higher number of MEs (1.34 (0.41), p = 0.002). More milk was removed with Pattern 2 (12.02 (5.66) g, p = 0.038) with a higher number of MEs (4.59 (1.91) g, p = 0.020). If the breast was fuller when pumped, creamatocrit post-expression (fuller: 13.7 ± 4.8%; emptier: 12.6 ± 4.2%; p = 0.037), DOF pre-expression (fuller: 0.82 ± 0.18; emptier: 0.62 ± 0.23; p < 0.001) and the volume of milk removed (fuller: 91 ± 54 g; emptier: 67 ± 44 g; p < 0.001) were higher. The efficacy ratios of milk removal were higher when the fuller breast was pumped: milk removal rate (fuller: 6.1 ± 3.6 g/min; emptier: 4.3 ± 2.9 g/min; p < 0.001), constant flow rate (fuller: 9.3 ± 4.7 g/min; emptier: 8.2 ± 4.5 g/min; p = 0.009), milk removed during constant flow (fuller: 79 ± 54 g; emptier: 57 ± 42 g; p < 0.001) and active milk removal (fuller: 8.4 ± 5.0 g/min; emptier: 6.8 ± 4.0 g/min; p < 0.001). The time when pumping could stop did not differ by the fullness of the breast (fuller: 11.6 ± 3.3 min; emptier: 11.7 ± 3.6 min; p = 0.45); however, when the fuller breast was pumped, more milk was expressed at time to stop (fuller: 85 ± 51 g; emptier: 64 ± 42 g; p < 0.001) with a higher efficacy ratio (fuller: 7.8 ± 4.9 g/min; emptier: 6.1 ± 4.4 g/min; p < 0.001).

Milk flow: Longer active flow durations (AFDs) and constant flow durations (CFDs) and higher efficacy ratios were associated with a higher PAMR (AFD: 1.83 (0.55)%, p = 0.002; CFD: 1.93 (0.56)%, p = 0.001) and a larger volume of milk removed (AFD: 3.22 (0.83) g, p < 0.001; CFD: 4.57 (0.68) g, p < 0.001). Milk volume removed at a late ME was positively associated with the total volume of milk removed (1.73 (0.60) g, p = 0.035). The maximum flow rate was higher (fuller: 0.47 ± 0.27 g/s; emptier: 0.43 ± 0.25 g/s; p = 0.012), and both AFDs (fuller: 11.2 ± 3.4 min; emptier: 10.3 ± 3.3 min; p = 0.005) and CFDs (fuller: 8.8 ± 4.2 min; emptier: 7.2 ± 3.6 min; p < 0.001) were longer when the fuller breast was pumped. However, overall and non-flow durations were not significantly different. Milk flow patterns did not differ significantly between sessions, but a higher number of MEs was observed when the fuller breast was pumped (fuller: 4.7 ± 1.6; emptier: 4.4 ± 1.5; p = 0.015). The time to the first milk flow (fuller: 0.69 ± 0.74 min; emptier: 1.04 ± 1.54 min; p = 0.035) and to the first ME (fuller: 1.12 ± 0.82 min; emptier: 1.66 ± 2.14 min; p = 0.028) were shorter.

Nipple temperature: Higher post-expression nipple temperatures (°C) were associated with Pattern 2 (0.06 (0.03), p = 0.037) and a higher number of MEs (0.25 (0.08), p = 0.003), as well as increased flow durations (overall flow duration: 0.11 (0.03) °C, p = 0.001; AFD: 0.07 (0.03) °C, p = 0.021; CFD: 0.06 (0.03) °C, p = 0.047; time to stop pumping: 0.08 (0.03) °C, p = 0.006; time to last ME: 0.11 (0.02) °C, p < 0.001; and time to late ME (0.20 (0.07) °C, p = 0.037). Higher post-expression nipple temperatures were also related to higher amounts of milk expressed (total milk removed: 0.005 (0.002) °C, p = 0.027; milk removed during CFD: 0.006 (0.003) °C, p = 0.016; milk at time to stop pumping: 0.006 (0.003) °C, p = 0.031; milk after time to stop: 0.09 (0.04) °C, p = 0.017 and higher efficacy ratio (milk removal rate, g/min): 0.08 (0.04) °C, p = 0.036).

Our findings show that the pre-expression degree of fullness of the breast drives most of the relationships with milk flow patterns and efficacy parameters. Further, pumping a fuller breast results in more milk removed and higher efficacy ratios; however, the overall flow duration time and PAMR are not affected, indicating that for individual women, breast drainage occurs at the same time regardless of the degree of breast fullness. Therefore, most mothers can pump for less than 15 min independent of the fullness of the breast to remove most of the available milk.