Table 3.

Diurnal cortisol

Birth group	Morning cortisol	Evening cortisol	Mean daily cortisol			Diurnal slope
	Geometric mean±SD*	Geometric mean±SD*	Geometric mean±SD*	Estimate of group effect Percentage (95% CI)†	P value	Geometric mean±SD‡	Estimated group differences in cortisol slope Percentage (95% CI)†	P value
Term (≥37 weeks), n=42	7.8±2.6	1.7±2.3	3.6±1.8	Reference		4.6±3.9	Reference
Preterm (≤32 weeks), n=48	4.1±2.4	1.7±2.6	2.7±1.8	−26.8 (−44.1 to −4.3)	0.02	2.3±3.9	−48.8 (−69.8 to −13.2)	0.01
Extremely preterm (<28 weeks), n=14	4.3±2.4	3.5±2.4	3.9±1.7	13.3 (−22.8 to 66.3)	0.52	1.2±3.8	−72.9 (−87.1 to −42.8)	<0.001
Very preterm (28–32 weeks), n=34	4.0±2.4	1.3±2.3	2.3±1.8	−36.6 (−52.4 to −15.6)	0.002	3.0±3.6	−33.6 (−62.0 to 16.0)	0.15

Analyses were conducted using log₁₀-transformed cortisol values.

*Mean morning, evening and daily log₁₀ cortisol values were back-transformed producing geometric means.

†Back-transformed regression coefficients represent percentage differences in cortisol metrics between groups.

‡ Diurnal slope representing the ratio of morning and evening geometric means was calculated through back transformation of mean log₁₀ (morning / evening) cortisol values.