Glucocorticoids are essential for fetal growth and organ development. During pregnancy, activation of the hypothalamic-pituitary-adrenal (HPA) axis drives an approximate threefold increase in serum cortisol concentrations compared with non-pregnant levels. Dysregulation of the HPA axis is associated with pregnancy complications and, in obese pregnancy, reduced HPA axis activity is associated with increased birthweight and prolonged gestation. Circadian (daily) regulation of the HPA axis is maintained in pregnancy, but whether ultradian (hourly) regulation of cortisol pulsatility changes across gestation is not known.

Stirrat et al. measured cortisol, cortisone, corticosterone and 11-dehydrocorticosterone in timed serum and interstitial fluid samples to investigate ultradian rhythms of glucocorticoid secretion across gestation in lean and obese pregnancies. They found that total daytime circulating maternal cortisol levels were increased with advancing gestation in lean but not in obese pregnancies. Notably, analysis of interstitial fluid cortisol levels identified that, compared with lean pregnancy, cortisol pulse frequency was significantly lower in obese pregnancy with advancing gestation.

These findings represent a novel mechanism that may explain decreased HPA activity in obese pregnancy.

Read the full article in Clinical Endocrinology doi:10.1111/cen.13548