In a new study, researchers found stress hormone cortisol is higher in women who give birth in the autumn and winter than those who give birth in the spring or summer.
This could explain why mental health disorders are more common in people born during the winter.
The research was conducted by a team from Cardiff University.
Seasonal changes in mood and behavior are commonly reported in the general population.
Previous research has shown that higher levels of cortisol in pregnant women are linked to a higher risk of children developing mental health disorders.
In the study, the team used data from the longitudinal Grown in Wales study to examine the link between the seasons and cortisol levels, depression and anxiety, birth weight and placenta weight in pregnant women. The data were from 316 women.
Data was gathered prior to and immediately after birth, through questionnaire and notes recorded by the research midwife. Cortisol levels were tested from maternal saliva samples.
The team found although maternal cortisol levels naturally rise during pregnancy, autumn and winter babies are exposed to particularly high levels just before they are born.
On average, women giving birth in the autumn/winter had 20% more cortisol just before delivery than those giving birth in spring/summer.
The new finding could explain why these disorders are more common in people born during the winter months.
This is no link between season and maternally-reported mental health symptoms, birth weight or placental weight.
Future research is needed to see why women who give birth in winter or autumn have these higher levels of cortisol.
One author of the study is Professor Ros John, from Cardiff University’s School of Biosciences.
The study is published in Psychoneuroendocrinology.
Copyright © 2019 Knowridge Science Report. All rights reserved.