Objectives
Measuring maternal milk production is cumbersome. Our objectives were to: 1) confirm that milk production rate reaches steady state at hour 2 of hourly breast emptying; and 2) compare agreement in milk production when measured using the well-established test-weighing method versus the more efficient hourly breast emptying method (Lai, et al., Breastfeeding Medicine, 2010).
Methods
Eligible mothers were 4–10 weeks postpartum and exclusively breastfeeding their healthy, singleton, term infants. A subset of mothers test-weighed (TW) their infant (± 2 g) before and after breastfeeding for 48h. Within 1 week of TW, mothers had a morning visit at the research clinic for hourly breast expression measurements. Mothers emptied both breasts at baseline (h0), and 1, 2, and 3 hours after baseline (h1, h2, h3) using a hospital-grade pump. We recorded hourly milk output ± 1 g and adjusted production rate (g/h) to exact interval (minutes from end of previous to end of current expression). We used paired t-test to compare g/h at h3 versus h0, h1, and h2. We estimated mother's steady-state milk production rate (MPR, g/h) as mean (h2, h3). We used the Bland-Altman method for determining the 95% limits of agreement in measuring milk production (g/24h) using TW versus MPRx24.
Results
23 mothers (65% primiparous) were 54 ± 14 days postpartum. Milk output was 185 ± 55 g at h0 and 60 ± 26, 47 ± 13, 44 ± 13 g/h at h1, h2, and h3, respectively. Mean paired difference (vs. h3) was significant at h0 and h1 (P < 0.05), but not at h2 (P > 0.05, h3 - h2 = 3 ± 10 g/h). In the subset with TW data (n = 16), mean TW milk output was 717 ± 119 g/24h, and mean MPRx24 was 1085 ± 300 g/24h. Mean difference, MPRx24 - TW [± 95% limits of agreement], was 368 [± 468] g/24h; and mean ratio, MPRx24/TW, was 1.5 [± 0.4]. Both difference and ratio significantly increased as MPR increased (P < 0.05).
Conclusions
Hourly milk production reaches steady state at h2; thus, mean (h2, h3) is a valid measure of current maternal milk production capacity. However, there was not homogeneous agreement between MPR and TW, and the 95% limits of agreement were very wide: -91 to 459 g/24h when expressed as the difference, and 0.9 to 1.9-fold as a ratio. Thus, MPR is feasible for researching variation in maternal milk production but not for researching variation in infant intake.
Funding Sources
None.
Supporting Tables, Images and/or Graphs