ESPE Abstracts

Background: In mammals, maternal glucocorticoids are transmitted through breast milk, particularly under stressful circumstances. In humans, it is unclear whether milk cortisol levels are dependent on stressful perinatal circumstances, such as preterm birth.

Objective and hypotheses: Our aim was to compare cortisol concentrations in breast milk of mothers of very preterm infants (GA <32 weeks) to breast milk cortisol concentrations of mothers of full-term infants (GA ≥37 weeks). We expected to find higher cortisol concentrations in preterm breast milk.

Methods: Breast milk samples from five preterm mothers and five full-term mothers were obtained weekly in the first month postpartum. After hexane extraction, cortisol concentrations were assessed by our extensively validated LC–MS/MS method. Longitudinal changes in cortisol concentrations, as well as the influence of time of collection, were analysed by generalised estimating equations. Results are shown as β (95% CI).

Results: No significant difference in cortisol concentration was found between groups: −31.7 (−72.4; 9.1), P=0.13. Concentrations were dependent on the time of collection, with the highest cortisol level between 0600 and 1200 h: 48.6 (45.3; 51.8), P<0.001.

Conclusions: We found no difference in cortisol level between preterm and full-term breast milk. Instead, our study provided evidence for diurnal rhythmicity in human milk cortisol concentration. To explore this further, we are now conducting a study in which healthy full-term mothers are requested to collect ten paired breast milk and saliva samples over 24 h. We hypothesise that cortisol concentrations in breast milk follow a diurnal rhythm, parallel to the salivary cortisol concentration.