Diurnal cortisol trajectories from mid-pregnancy to one year after birth

The hypothalamic-pituitary-adrenal (HPA) axis is involved in the regulation of pregnancy and postpartum recovery. Diurnal cortisol indices, specifically cortisol awakening response (CAR), area under the curve (AUCg), and slope, are ways to study HPA axis activity. Whether these indices show within-person changes during the perinatal period is not clear, nor do we know how maternal sociodemographic, health, or prenatal medical conditions are associated with within-person diurnal cortisol index trajectories. The purpose of this study is to investigate within-person changes in three diurnal cortisol indices from mid-pregnancy to one year postpartum, and test whether sociodemographic, pregnancy, or health factors moderate these changes.

A sample of 172 pregnant women provided saliva samples at six time points from mid-pregnancy to one year after birth. At each time point, they provided samples on two days (wake, 30 + wake, noon, pm). The samples were assayed for cortisol. CAR, slope and AUCg indices were calculated. Piecewise growth curve models tested for within-person changes during pregnancy and postpartum on each index with sociodemographic, pregnancy and health variables included in the models.

Within-person trajectories were observed only for AUCg during pregnancy, linear: b = -0.51, p = .012; quadratic: b = -0.45, p = .009, such that AUCg increased from mid to late pregnancy. No significant within-person changes in CAR or slope were observed in pregnancy or after birth. Hispanic women demonstrated increasing CAR in the postpartum year, whereas the opposite was observed for non-Hispanic women. Longer gestation was associated with increasing AUCg after birth.

AUCg increased from mid-to-late pregnancy, consistent with prior research. Maternal ethnicity and gestational length moderated diurnal cortisol index trajectories during the postpartum period only.