Determinants of maternal hair cortisol concentrations at delivery reflecting the last trimester of pregnancy.

Hair cortisol concentrations (HCC) are emerging as a promising marker of chronic psychosocial stress. However, limited information on relevant correlates of this biomarker in late pregnancy is available. In the Ulm SPATZ Health Study mothers were recruited between 04/2012 and 05/2013 shortly after delivery in the University Medical Center Ulm, Germany. Cortisol concentrations of N=768 participants were determined by HPLC-MS/MS in the scalp-near 3cm of maternal hair reflecting stress exposure over the preceding three months. Sociodemographic characteristics, pregnancy-related variables and comorbidities were assessed. We conducted bivariate and multiple linear regression analyses using log transformed HCC. In bivariate analyses, significantly higher cortisol concentrations were found in obese compared to normal weight (b=0.32, p<0.001) and smoking as opposed to non-smoking mothers (b=0.34, p=0.002). Conversely, primary C-section was associated with lower HCC compared to spontaneous delivery. Besides, a strong impact of season of delivery with significantly higher HCC in summer and autumn as opposed to winter (both bs=0.58, p<0.001) was found. Further determinants of HCC were maternal education, number of persons in the household, premature delivery and hair characteristics. In a mutually adjusted model, all but education, multiple jobholding, hair characteristics and premature delivery remained statistically significant. Maternal hair cortisol in the last trimester of pregnancy is determined by many factors. Delivery mode, body mass index and season of delivery should be considered when investigating the association between HCC and further outcomes in mothers shortly after delivery.