Bibian van der Voorn

76 CHAPTER 6 ABSTRACT BACKGROUND Very preterm infants often receive donor milk from mothers who deliver at term, but its composition differs from that of their own mothers milk. Because breast-milk glucocorticoidscansupportdevelopingneonates,weexploredconcentrationvariability within and between mothers. We hypothesized that breast-milk glucocorticoid concentrations would be higher after very preterm delivery (GA <32 wks; study 1) and would follow the diurnal rhythm of maternal adrenocortical activity (study 2). METHODS Study 1 assessed differences in milk cortisol, cortisone, and the cortisone-to- (cortisol+cortisone) ratio of mothers who delivered at (median) GA: 28.6 wk or at term weekly during the first month postpartum. Study 2 assessed variations in milk cortisol, cortisone, and the cortisone-to- (cortisol+cortisone) ratio over 24 h, and tested Pearson correlations between milk and salivary concentrations in mothers who delivered at term (median GA: 38.9 wk) during week 4 postpartum. In these studies, foremilk glucocorticoids were measured by LC-MS/MS. Associations of milk cortisol, milk cortisone, and the milk cortisone-to-(cortisol+cortisone) ratio with prematurity (study 1) or collection time (study 2) were studied with longitudinal data analyses. RESULTS In study 1, giving birth to a very preterm infant was associated with reductions in milk cortisol and cortisone concentrations of 50% (β: 0.50; 95%CI: 0.26, 0.99; P = 0.05) and 53%( β: 0.53; 95%CI: 0.30, 0.93; P = 0.03), respectively, when adjusted for collection time. In study 2, concentrations of milk cortisol and cortisone were associated with collection time (both P < 0.01), peaking at ∼0700.Milk and salivary concentrations of cortisol (r = 0.92, P < 0.01) and cortisone (r = 0.93, P < 0.01) as well as the cortisone- to-(cortisol+cortisone) ratio (r = 0.64, P < 0.01) were correlated with one another. CONCLUSIONS Breast-milk glucocorticoid concentrations follow the diurnal rhythm of maternal HPA axis activity and are lower in mothers who deliver very preterm. b g i w c d e f t ( a i d I M o n m 9 collecti me. I collecti me < cor 01 a