Trends in hair cortisol from preconception to the postpartum period.

Introduction: Cortisol is a biological marker of stress, and its levels reflect the hypothalamic-pituitary-adrenal (HPA) axis response to stress over time. Saliva, blood, and urine cortisol reflect acute stress, whereas assessment of hair cortisol is a better reflection of chronic stress. There is limited information on hair cortisol concentration (HCC) in the perinatal period, particularly, in the preconception and postpartum periods. In addition to being a biomarker for stress, high levels of cortisol are typically associated with poor psychosocial outcomes, and adverse pregnancy outcomes. The objectives of this study were: (1) to measure HCC from six months preconception to six months postpartum; (2) to examine the relationship between HCC and demographic characteristics, depressive symptoms, and perceived stress in the first six months postpartum period; (3) and to assess the associations between HCC and systemic inflammatory markers in the first six months postpartum.

Methods: The analysis included 96 women from a longitudinal study with up to 3 study visits in the first six months postpartum. Blood and hair samples were collected at 1-2 months (PP1), 3-4 months (PP2), and 5-6 months (PP3) postpartum. We obtained sociodemographic information, depressive symptoms, and perceived stress scores at PP1-PP3. To quantify cortisol levels over time, 8 segments were derived corresponding to 6 (PC1) and 3 (PC2) months preconception as well as for each trimester (T1-T3) and postpartum (PP1-PP3). Eight cytokines (Granulocyte-macrophage colony-stimulating factor (GM-CSF), Interferon- gamma [IFN- γ], Interleukin [IL]-10, IL-2, IL-4, IL-6, IL-8, and Tumor necrosis factor-alpha (TNF- α) were measured in plasma in the postpartum samples. Univariate, bivariate, correlations, and linear mixed modelling were performed using SAS 9.4. Multiple testing correction was conducted for correlations using false discovery rate and a Q value of <0.05 was deemed significant.

Results: Median HCC varied over time peaking in the third trimester and declining in the postpartum. Significant differences were noted in median cortisol levels by race with Black/African American postpartum women experiencing higher levels at all timepoints. Significantly, higher median cortisol levels were also observed at PP1 and PP2 for mothers who reported their relationship status as single. Ethnicity, education, median age, depressive symptoms, and perceived stress were not associated with median cortisol levels. Pro-inflammatory cytokines IFN- γ (q= 0.01; r=-0.50) and IL-8 (q= 0.00; r=-0.55) showed correlations with HCC at PP1.

Conclusion: HCC increased during pregnancy, peaking at T3 and declining PP consistent with previous work. Black/African American women and single women have significantly higher median cortisol levels in the postpartum period. The marked increase of HCC in Black women may be an important factor in understanding maternal health racial inequities. Future studies should investigate how the relationships between HCC, sociodemographics, and systemic cytokines impact perinatal outcomes.