The maternal cortisol awakening response in human pregnancy is associated with the length of gestation.

Objective: The purpose of this study was to examine the relationship between intraindividual changes in cortisol responsiveness over pregnancy and the length of human gestation.
Study Design: Pregnancy-related changes in the cortisol awakening response (CAR), which is a measure of hypothalamic-pituitary-adrenal axis responsiveness, were assessed prospectively in 101 pregnant women at 16.8 +/- 1.4 weeks' and 31.4 +/- 1.3 weeks' (+/-SD) gestation. Cortisol was measured in saliva that was collected immediately and +30, +45 and +60 minutes after awakening.
Results: The CAR was significant in pregnancy and exhibited progressive attenuation over the course of gestation. A larger CAR in late pregnancy and reduced attenuation of the CAR from early to late gestation were associated significantly with shorter gestational length.
Conclusion: The findings are the first to suggest that the hormonal (cortisol) response to a naturally occurring challenge (awakening) and the degree of attenuation of this response over the course of gestation may represent a novel biomarker of increased vulnerability for earlier birth.