Determination of nighttime salivary cortisol during pregnancy: comparison with values in non-pregnancy and Cushing's disease

Purpose Nighttime salivary cortisol (NSC) has been proposed for the diagnosis of Cushing's syndrome during pregnancy. However, reference values for NCS in pregnant women have not been adequately determined. The aim of this study was to determine the reference values of NSC in the three gestational trimesters in order to help distinguish physiological from pathological hypercortisolism during pregnancy. Methods This prospective and retrospective study evaluated 85 pregnant women in whom samples were collected in the first, second and/or third gestational trimester (pregnancy group), 33 non-pregnant women (control group), and 25 non-pregnant women with Cushing's disease (CD group). NSC was measured by enzyme-linked immunosorbent assay. Results NSC increased progressively during pregnancy, reaching maximum levels on the third trimester (median 2.1-fold increase compared with controls, p< 0.001). Reference values for NSC were determined and the upper limits on each gestational trimester were: first trimester 0.25 mu g/dL (6.9 nmol/L), second trimester 0.26 mu g/dL (7.2 nmol/L), and third trimester 0.33 mu g/dL (9.1 nmol/L). Cutoff values that separated the CD group from the three trimesters in the pregnancy groups were, respectively, 0.255 mu g/dL (7.0 nmol/L), 0.260 mu g/dL (7.2 nmol/L), and 0.285 mu g/dL (7.9 nmol/L). Comparison of NSC cutoff values in pregnant women with CD patients showed high sensitivity and specificity in all three trimesters. Conclusions We established cutoff values for determination of NSC which can be useful for pregnant women with a diagnostic suspicion of CD.