Pregnant women who have a higher level of a hormone produced in the placenta have a higher likelihood of developing post-partum depression, according to a new study from the University of California in Irvine.

The researchers took blood samples from 100 pregnant women when they were 15, 19, 25, 31 and 37 weeks pregnant. During follow-up visits, 16 of the women were found to have developed the so-called "baby blues" in the weeks after their babies were born.

According to the researchers, levels of placental coriticotropin-releasing hormones, or pCRH, were higher in these women during pregnancy than in the other subjects.

The researchers said that based on this initial research, 76 percent of the women who develop post-partum depression could be accurately pre-diagnosed for the disorder if doctors test their pCRH levels.

They said if their work can be replicated, pCRH screening could one day be added to pre-natal treatment.

The study was published in the Archives of General Psychiatry.