Extremely and very preterm children who were born appropriate for gestational age show no differences in cortisol concentrations or diurnal rhythms compared to full-term children.

OBJECTIVES: The objective of this study was to compare the diurnal variations in cortisol and cortisone concentrations in serum and saliva among extremely preterm (EPT), very preterm (VPT), and full-term (FT) children, all born appropriate for gestational age (AGA). METHODS: EPT, VPT, and FT children, all born AGA, were recruited from two healthcare centers. Cortisol and cortisone concentrations in serum and saliva were measured by liquid chromatography-mass spectrometry (LC‒MS). Statistical analysis was performed using nonparametric tests. RESULTS: A total of 101 children (5.0-8.9 years old) were included in this study: EPT=18, VPT=43 and FT=40. All groups had similar distributions in terms of age, birth weight standard deviation score (SDS) and BMI (SDS), showing no differences in serum ACTH, cortisol, or cortisone levels. Additionally, salivary cortisol and cortisone concentrations decreased significantly throughout the day (p-values<0.0001). Salivary cortisol concentrations were below the limit of detection (0.55 nmol/L) before dinner and before bedtime in approximately one-third and two-thirds of all children, respectively. Salivary cortisone was detectable in all but one sample. CONCLUSIONS: The diurnal cortisol rhythm was preserved in all preterm children, regardless of their gestational age, and no differences in cortisol concentrations among the groups were found. This may have significant implications for the clinical management and follow-up of preterm individuals.