Chatterton et al¹ addressed these issues in a prospective study of 39 mothers delivering preterm infants (<1500 gms and 30 wks gestation at birth) who were approached within 48 hrs after delivery and carefully instructed on a standardized milk pumping protocol either with a single or double collection kit and a Medela 016 Lactina breast pump. The purpose of their study was 2-fold: 1) to determine the relationship between milk production and prolactin (PRL) and oxytocin levels over time during mechanical breast stimulation, and 2) to examine the relationship between milk production, PRL, and oxytocin levels and measures of stress (salivary cortisol and α-amylase, Multiple Affect Adjective Checklist-Revised (MAACL-R)) up to 6 weeks post-partum.

1. Milk production in the first week of breast pumping was not related to gestational age at delivery and was similar to milk production after a term pregnancy.
2. Milk production increased significantly across the 6-week period, but the variation was extremely wide.
3. In the 6th week of the study the women producing the most milk were pumping 42.3 times per week (~ 6 times/day) versus 30.6 times per week (~4.4 times/day) for women producing less.
4. When graphed, double pumping appeared to produce more milk at each time period (1-6 weeks), but the difference was not statistically significant. Double-pumping did significantly increase PRL concentrations (43 ng/mL vs. 73 ng/mL (p=0.002) after 20 minutes of pumping. Oxytocin was increased by double pumping at week 6.
5. There was no correlation between PRL levels and milk volume.
6. There was a positive correlation between oxytocin and milk volume, but no correlation with measures of stress.

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