Women living in large cities in Canada have a higher risk of post-partum depression than women in less populated areas, a new study has found.

Post-partum depression can begin shortly after a woman gives birth. It’s not clear why some new mothers develop it and others do not, but risk factors include a history of depression and lack of social support.

This latest study, based on a 2006 national survey of almost 6,500 new mothers, found that the overall prevalence of post-partum depression was about 7.5 per cent. But among mothers living in cities with a population of at least 500,000, almost 10 per cent reported experiencing post-partum depression.

That is compared with six per cent of new mothers in rural areas, almost seven per cent in semi-rural areas and about five per cent in semi-urban areas.

The authors of the study note that big cities tend to have higher numbers of recent immigrants, and more urban-dwelling women in this study reported lower levels of social support during and after pregnancy than women living in other areas.

"The risk factors for post-partum depression (including history of depression, social support and immigration status) that were unequally distributed across geographic regions accounted for most of the variance in the rates of post-partum depression," the authors write.

Dr. Simone Vigod, the lead researcher and a psychiatrist at Women's College Hospital, says it’s important to spot women suffering from this form of depression, because ignoring it can lead to tragic consequences.

"This is a treatable illness and we can prevent or reverse problems that are starting to develop," she told CTV News.

Giovanna Vaccaro is one of thousands of women who struggled after the birth of her baby, Emma, with intense feelings of anxiety and sadness.

“I thought I just needed some sleep. I wasn’t getting a lot of that and I couldn’t turn my brain off. And I thought that if I could just get some sleep, everything would be fine," she remembers.

Giovanna is now getting help through counselling and medications, .and it's working.

“I'm really enjoying my child right now and I wasn't at the beginning, because you feel so overwhelmed," she says.

The authors say the study suggests that there’s a strong need for services designed to help isolated women in big cities increase their social connections.

"Considering the substantial negative effect of post-partum depression, such interventions could have a broad-reaching social and public health impact,” write the authors.

In Canada, about 35 per cent of the population lives in the large urban areas of Montreal, Toronto and Vancouver, about 20 per cent live in rural or remote regions, and the rest live in smaller urban or semirural settings.

The study, which appears in the Canadian Medical Association Journal, was conducted by researchers from Women's College Hospital, Centre for Addiction and Mental Health, St. Michael's Hospital and the University of Toronto, along with researchers from Midwives Grey Bruce in Owen Sound, Ont.