Circadian cortisol dynamics across reproductive stages and in relation to breastfeeding in the Philippines.

Objective: An increase in cortisol during human pregnancy helps coordinate the onset of parturition, and can have long-term effects on offspring biology. Maternal cortisol can also be transferred to offspring via breast milk during lactation. However, little is known about how diurnal cortisol profiles vary by trimester of pregnancy or during the postpartum period. Here, we describe diurnal cortisol profiles among a large cross-sectional sample of healthy Filipino young adult women varying in reproductive status and, during the postpartum period, in whether or not they are breastfeeding.

Methods: Salivary cortisol, anthropometric, and questionnaire data were obtained from participants in a birth cohort in metropolitan Cebu, Philippines (N = 741; age 20.8-22.4 years). Cortisol was assessed at waking, thirty minutes after waking (cortisol awakening response, CAR), and before bed.

Results: Compared with nulliparous women, morning cortisol was roughly 50% higher among women in late gestation, while evening cortisol was roughly 4-fold higher and the CAR was lower. Postpartum waking and evening cortisol were lower among currently breastfeeding women compared to nulliparous women, but were comparable in the absence of breastfeeding. The CAR was significantly lower among postpartum women compared to nulliparous women irrespective of breastfeeding status.

Conclusions: These findings are consistent with known alterations in hypothalamic-pituitary-adrenal axis function during reproduction, and in particular point to marked and progressive elevation in maternal cortisol during the course of gestation. Cortisol appears to return to nulliparous levels after parturition, with levels suppressed below nulliparous levels during lactation.