Study: Infants secrete different stress hormone than their mothers during labor and delivery

During labor and delivery, infants preferentially secrete a different stress hormone than their mothers do, according to a new clinical study. The results will be presented Saturday at The Endocrine Society's 95th Annual Meeting in San Francisco and published in the open access journal, PLoS One.

A primary component of good pregnancy care is the ability to quickly recognize and respond to fetal distress. Since the stress hormone cortisol is found in much higher concentrations than the hormone corticosterone, it has received greater attention as an indicator of stress in both mothers and newborns. At the same time, the role of cortisol's less well-known relative, corticosterone, in signaling fetal distress has remained unclear.

In this study, investigators found compared the concentrations of hormones in the umbilical artery and umbilical vein to assess the hormones added to the circulation by the baby. Corticosterone increased during labor and delivery at a significantly greater rate compared to cortisol, although overall cortisol levels were still higher. Specifically, corticosterone concentrations increased by 148 percent, compared to 49 percent for cortisol. As fetal stress increased, so did corticosterone concentrations.

"Fetal corticosterone could serve as a biomarker of fetal stress," said study lead author Katherine E. Wynne-Edwards, PhD, Jack Manns Professor of Comparative Endocrinology at the University of Calgary in Calgary, Alberta, Canada.

Corticosterone concentrations also varied according to whether the delivery was vaginal or surgical. Compared to infants delivered by Caesarian section, vaginally delivered infants synthesized greater concentrations of corticosterone. When Caesarian delivery occurred because the baby's head was too large to pass through the birth canal, which was expected to be a stressor on the baby, the highest corticosterone concentrations were seen. On the other hand, interventions to strengthen maternal contractions did not increase corticosterone concentrations.

"Newborn corticosterone synthesis might be the basis for a signal to the mother that the baby is in distress, and might also indicate that a previously unsuspected developmental transition from preferential corticosterone synthesis to preferential cortisol synthesis occurs in early life," Wynne-Edwards said. "If so, then corticosterone might be an important biomarker of adrenal function in premature infants that is not yet studied or understood."

Investigators compared blood concentrations of corticosterone and cortisol, quantified by mass spectrometry, from 300 participants admitted for labor and delivery. After excluding mothers who delivered pre-term or multiple births, investigators analyzed umbilical cord blood samples from 265 healthy deliveries.