Women who live in large urban areas are more likely than their peers in more rural areas to develop postpartum depression, according to new research from Canada.

That's largely because risk factors for postpartum depression - such as having low levels of social support and being born outside of the country - are more common among women living in urban areas, Dr. Simone Vigod, from the Women's College Research Institute in Toronto, and her colleagues found.

Many women may feel moody, anxious and tearful in the first couple of weeks after having a baby, thanks to hormonal shifts, lack of sleep and new-parent stress. When these symptoms get better on their own in a few days, they're known as "baby blues."

But between 10 and 15 percent of women develop persistent, serious depression during the first year after their baby's birth, according to the U.S. Centers for Disease Control and Prevention.

Vigod and her team looked at data from a 2006 survey of 6,126 new mothers to determine whether where they lived might influence their postpartum depression risk.

About 7.5 percent of all women surveyed reported depression symptoms that put them above the cutoff for postpartum depression, according to findings published in the Canadian medical journal CMAJ.

Just over nine percent of women living in cities of 500,000 people or more had postpartum depression, versus six percent of women living in rural areas - towns with less than 1,000 people.

Between five and seven percent of women living in suburban areas reported being depressed after giving birth.

"That's a pretty big difference at the population level," Vigod told Reuters Health.

"It's not the air that you breathe in an urban area that makes you depressed," she added, "it's actually that the population characteristics of people living there are different."

Specifically, Vigod and her colleagues found that urban women were less likely to report having adequate social support during pregnancy and after giving birth, and were also less likely to say they were in excellent or very good health. By taking these and other differences into account, the researchers were able to explain the higher depression risk among the urban women.

However, known risk factors for postpartum depression could not completely account for why the risk was lower among women living in certain suburban areas versus urban areas.

Women in the study were surveyed at five to 14 months postpartum, Vigod noted, so they weren't just suffering from a brief bout of baby blues. Ideally, she added, doctors would be able to identify at-risk women during pregnancy, in order to prevent them from becoming depressed after delivery.

"Perhaps social support should be assessed a little bit more explicitly than it is now," Vigod said. "For women at risk it's such a strong variable. Perhaps it's worth the cost of trying to increase social support systems."

Doctors could also go beyond simply asking pregnant women about their marital status, she added, and ask them in more detail about who will be on hand for them once the baby is born, and what the nature of that support will be.

Women born outside Canada may also face language and cultural barriers to accessing care there during pregnancy, Vigod pointed out.

"We live in a really multicultural society, people from all over the world live in Canada, and maybe there has to be special attention to the cultural context in order to really target depression."