A test could be developed to predict the likelihood of postnatal depression in new mothers by measuring hormone levels in the placenta, research suggests.
A study from the University of California found that a "surge" of placental corticotropin-releasing hormone (pCRH) between 23 and 26 weeks was strongly associated with postnatal or "postpartum" depression.
The condition, which severely affects around one in 500 new mothers, usually shows itself four to six weeks after giving birth and can, in extreme cases, lead to suicide or infanticide.
Scientists monitored levels of pCRH in 100 pregnant women and found that 16 went on to develop symptoms of postnatal depression.
When their levels of pCRH were examined, it was found that within a narrow band of pregnancy the hormone gave a good indication of risk.
The findings, reported in the journal Archives of General Psychiatry, showed that the hormone could be used to identify about three quarters of pregnant women expected to suffer from postnatal depression.
Evidence suggests that elevated levels of the stress hormone cortisol early in pregnancy may be the reason for increases in pCRH levels.