Women who have lower levels of the brain chemical oxytocin toward the end of their pregnancy may be more prone to develop postpartum depression than expecting moms with higher levels, a new study suggests.

Updated May 11, 2011

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By Amanda Gardner

WEDNESDAY, May 11, 2011 (Health.com) — Women who have lower levels of the brain chemical oxytocin toward the end of their pregnancy may be more prone to develop postpartum depression than expecting moms with higher levels, a new study suggests.

Known as the "love hormone" or "cuddle hormone," oxytocin is released during human-to-human contact (such as breast-feeding) and is critical to mother-baby bonding. Previous studies have shown that women whose oxytocin levels rise during pregnancy are more attached to their babies, but this is the first study to suggest a link with postpartum depression, which affects roughly 1 in 5 women.

Researchers in Switzerland measured the amount of oxytocin in blood samples taken from pregnant women during their third trimester, and found that women with lower levels were more likely to report symptoms of depression within two weeks of giving birth.

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The study was small, and more research will be needed to flesh out the relationship between oxytocin and postpartum mood. If the link is confirmed, however, oxytocin could provide a new way of identifying pregnant women who are at risk, so as to give them appropriate preventive care.

"It would be nice to know which women are more vulnerable," says Alan Manevitz, MD, a clinical family psychiatrist at Lenox Hill Hospital, in New York City, who was not involved in the study. "We could watch them more thoughtfully."

The researchers aren't sure why low oxytocin levels might increase the risk of postpartum depression, but they have some guesses. For instance, the hormone is known to reduce stress and feelings of fear, which aren't exactly uncommon in new parents.

"This may be of special relevance during the postpartum period, says the lead author of the study, Gunther Meinlschmidt, PhD, an assistant professor of psychology at the University of Basel. "During this time, the mothers are challenged by a bulk of potentially stressful—and in some cases fear-promoting—new conditions and demands."

Moreover, animal studies suggest that low oxytocin levels may interfere with a mother's feelings of closeness to her baby, which can contribute to postpartum depression, Meinlschmidt says.

Salih Yasin, MD, the chairman of ob-gyn at the University of Miami Miller School of Medicine, stresses that even if these theories are borne out, oxytocin is far from the only culprit that can influence a mother's mood after birth.

"Postpartum depression has so many factors," Yasin says. "Some of it has to do with socioeconomic status, the stress levels, the family history, previous depressive symptoms, the presence or absence of other medical conditions."

In the study, which appears in the journal Neuropsychopharmacology, Meinlschmidt and his colleagues analyzed blood samples from 73 healthy pregnant women. Women with a recent history of depression were excluded, although 16 did report experiencing some depression at some point more than two years before the start of the study.

Within two weeks of giving birth, the women answered a questionnaire designed to screen for depression symptoms. The women whose responses indicated a risk for postpartum depression had substantially lower oxytocin levels than the women who showed no signs of depression.

Dr. Manevitz says the findings would have been stronger had the researchers followed the women longer and used the official diagnostic criteria for postpartum depression, a persistent low mood that interferes with your ability to function for at least two weeks. (Any depression within the first year after birth is considered postpartum.)

"The mothers could have postpartum blues," he explains. That condition, also known as the "baby blues," is more common than full-blown postpartum depression and is often a short-lived response to lack of sleep, discomfort following labor, and other stresses.