The discovery could help identify and treat women at risk for postpartum depression long before the onset of symptoms.
Ilona Yim, psychology and social behavior assistant professor, and colleagues found that women whose levels of corticotrophin-releasing hormone started to increase more rapidly around 25 weeks of gestation had a higher incidence of postpartum depression.
Normally secreted in very small amounts by the hypothalamus, this hormone regulates the body's response to stress. During pregnancy, large amounts are produced in the placenta and are associated with delivery.
"The hormone we studied plays an important part in pregnancy and has been linked to depression," Yim said. "Many factors may cause some women's bodies to produce more of this hormone during pregnancy. Evidence suggests that stress early in pregnancy could play a role."
The researchers studied the hormone-postpartum depression link using data from a larger study funded by the National Institute of Child Health and Human Development. They took blood samples from 100 pregnant women and assessed symptoms of depression throughout pregnancy, then again nine weeks after delivery.
Of the 100 women, 16 developed postpartum depression symptoms during follow-up visits. Three-fourths of those women, the study concludes, could have been identified in mid-pregnancy based solely on hormone levels.