Bibian van der Voorn

81 MILK GLUCOCORTICOID DIURNAL RHYTHMICITY Table 2 shows the breast-milk cortisol and cortisone concentrations for both groups. During the first month postpartum, the median concentrations (ranges) in milk from mothers who delivered at termwere 4.3 nmol/L (1.7 to 12.5 nmol/L) for cortisol, 29.6 nmol/L (15.9 to 44.0 nmol/L) or cortisone, and 0.86 (0.82 to 0.91) for the cortisone- to-(cortisol + cortisone) ratio. In milk from mothers who delivered very preterm the corresponding values were 3.2 nmol/L (1.1 to 6.1 nmol/L) for cortisol, 20.5 nmol/L (7.5 to 35.3 nmol/L) for cortisone, and 0.87 (0.82 to 0.91) for the cortisone-to- (cortisol + cortisone) ratio. No differences were found between very preterm and term milk samples in cortisol (β: 0.59; 95% CI: 0.25 to 1.40; P = 0.23), cortisone (β: 0.60; 95% CI: 0.30 to 1.18; P = 0.14), or the cortisone-to-(cortisol + cortisone) ratio (β: 1.02; 95% CI: 0.96 to 1.08; P = 0.57) when assessed by GEE over time. When visually plotting the milk cortisol and cortisone concentrations with collection time, regardless of postnatal age, we found a pattern suggestive of diurnal rhythmicity (data not shown). Collection time was strongly associated with milk cortisol concentration (β: 0.90; 95% CI: 0.86 to 0.95), milk cortisone concentration (β: 0.94; 95% CI: 0.91 to 0.98), and the milk cortisone- to-(cortisol + cortisone) ratio (β: 1.01; 95% CI: 1.00 to 1.01) (all P < 0.01), when assessed by GEE. When adjusted for collection time, 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 to 0.99; P = 0.05) and 53% (β: 0.53; 95% CI: 0.30 to 0.93; P = 0.03), respectively. The milk cortisone-to-(cortisol + cortisone) ratio was not related to prematurity. TABLE 2. Glucocorticoid concentrations in breast milk of mothers who delivered very preterm vs. those who delivered at term: Study 1 1wk postpartum 2wk postpartum 3wk postpartum 4wk postpartum Preterm Term Preterm Term Preterm Term Preterm Term n = 10 n = 10 n = 10 n = 10 n = 10 n = 7 n = 9 n = 9 Cortisol 1.2 (0.4 to 5.1) 2.5 (1.3 to 12.9) 3.2 (1.1 to 4.8) 4.3 (1.3 to 10.9) 4.0 (1.0 to 8.5) 5.2 (2.1 to 11.2) 5.6 (2.4 to 14.8) 4.6 (1.7 to 15.6) Cortisone 15.5 (3.0 to 35.2) 31.2 (14.4 to 58.3) 22.8 (8.3 to 33.5) 27.9 (16.8 to 48.8) 22.0 (6.0 to 38.0) 38.5 (15.5 to 40.0) 20.5 (11.6 to 39.3) 29.8 (11.3 to 43.2) Ratio 0.92 (0.89 to 0.93) 0.91 (0.83 to 0.94) 0.87 (0.85 to 0.90) 0.87 (0.82 to 0.90) 0.86 (0.82 to 0.88) 0.87 (0.78 to 0.92) 0.80 (0.72 to 0.85) 0.82 (0.73 to 0.88) Values are median (IQRs). Unit of measurement is nmol/L. Ratio is calculated as Cortisone/ (Cortisol + Cortisone) No significant differences over time between preterm and term samples in milk cortisol, milk cortisone, or the cortisone-to-(cortisol+cortisone) ratio were observed. Study 2. Table 3 presents the baseline characteristics of the mothers who delivered at term. The mean 6 SD interval between sample collections was 3:21 6 1:23 h. Figure 2 shows diurnal variations in milk cortisol and cortisone concentrations and those of the cortisone-to-(cortisol + cortisone) ratio during week 4 postpartum. Peak milk cortisol and cortisone concentrations were reached at ∼0700. At the same time, a nadir was observed for the milk cortisone-to-(cortisol + cortisone) ratio.