Identifying women at risk for postpartum depression might be as easy as measuring hormone levels in the blood during pregnancy, suggests a study published today in the Archives of General Psychiatry.

"We found a hormone that is produced by the placenta during pregnancy that is a good predictor of postpartum depression," says lead author Ilona Yim, a psychologist at the University of California in Irvine. Using blood tests to measure this hormone might one day help doctors identify mothers-to-be at risk for postpartum depression (PPD).

After childbirth, many women suffer from the "baby blues"—mood swings, anxiety, sadness, and difficulty sleeping that typically clear up within 10 days. But some new moms suffer from PPD that can last for months and often requires psychotherapy and/or antidepressants.

The U.S. Department of Health and Human Services estimates that some 13 percent of women in the U.S. suffer from depression during pregnancy and/or in the weeks or months following childbirth; some studies put the number higher, suggesting PPD affects up to 19 percent of mothers. There are certain risk factors associated with PPD, including a history of mental illness and drug and alcohol abuse.

Yim and her colleagues followed 100 pregnant women in southern California throughout their pregnancies and for approximately nine weeks after their babies were born.

The researchers at five intervals (15, 19, 25, 31 and 37 weeks) tested their subjects' blood levels of placental corticotropin-releasing hormone (pCRH), a hormone that normally climbs during pregnancy to prepare the body for birth and that they suspected might be linked to PPD.

About nine weeks after each woman delivered, the scientists asked each one to complete a survey on whether she had any PPD symptoms. The researchers discovered that the women who developed PPD all had a surge of pCRH on or around their 25th week of pregnancy; 75 percent of the 16 women identified with the condition had more than 56.86 picograms per milliliter of pCRH in their blood compared with only 24 percent of those who did not develop PPD.

Yim says she's optimistic that further research may confirm her findings and that pCRH may one day be used to predict postpartum depression.