It's no secret that pregnancy hormones can dampen moods, but for some expectant moms, it's much worse: 1 in 5 experience major depression.

Now, new research shows that an age-old recommended stress-buster may actually work for this group of women: yoga.

Pregnant women who were identified as psychiatrically high risk and who participated in a 10-week mindfulness yoga intervention saw significant reductions in depressive symptoms, according to a University of Michigan Health System pilot feasibility study. Mothers-to-be also reported stronger attachment to their babies in the womb.

The findings were published in Complementary Therapies in Clinical Practice.

"We hear about pregnant women trying yoga to reduce stress but there's no data on how effective this method is," says lead author Maria Muzik, M.D., M.S., assistant professor of psychiatry and assistant research scientist at the Center for Human Growth and Development. "Our work provides promising first evidence that mindfulness yoga may be an effective alternative to pharmaceutical treatment for pregnant women showing signs of depression.

"This promotes both mother and baby wellbeing."

Mental health disorders during pregnancy, including depression and anxiety, have become a serious health concern. Hormonal changes, genetic predisposition and social factors set the stage for some expectant moms to experience persistent irritability, feelings of being overwhelmed and inability to cope with stress.

Untreated, these symptoms bear major health risks for both the mom and baby, including poor weight gain, preeclampsia, premature labor and trouble bonding with the new baby.

While antidepressants have proven to effectively treat these mood disorders, Muzik says, previous studies show that many pregnant women are reluctant to take these drugs out of concern for their infant's safety.

"Unfortunately, few women suffering from perinatal health disorders receive treatment, exposing them and their child to the negative impact of psychiatric illness during one of the most vulnerable times," Muzik says. "That's why developing feasible alternatives for treatment is critical."

Evidence suggests women are more comfortable with nontraditional treatments, including herbal medicine, relaxation techniques and mind-body work.

Yoga continues to grow in popularity but in the United States, many classes concentrate on yoga as "exercise," omitting the practice of being fully present in the moment and aware, authors say.

Meanwhile, mindfulness yoga - which combines meditative focus with physical poses - has proven to be a powerful method to fight stress and boost energy.

For the U-M research study, women who showed signs of depression and who were between 12-26 weeks pregnant participated in 90-minute mindfulness yoga sessions that focused on poses for the pregnant body, as well as support in the awareness of how their bodies were changing to help their babies grow.

Funding for follow up work on this subject was recently provided by a grant from the Institute for Research on Women and Gender.

"Research on the impact of mindfulness yoga on pregnant women is limited but encouraging," Muzik says. "This study builds the foundation for further research on how yoga may lead to an empowered and positive feeling toward pregnancy."