Postpartum depression can occur after a woman has given birth and is a serious health risk for both women and their babies. The symptoms are more intense and longer lasting than the typical baby blues and may eventually interfere with a mother's ability to care for her child.
The study, published Monday in the Canadian Medical Association Journal, is based on a 2006 national survey of almost 6,500 new mothers. It found that almost 10 per cent of the women living in cities with a population of at least 500,000 reported experiencing postpartum depression.
That compares with six per cent of new moms in rural areas, almost seven per cent in semi-rural, or small-town areas, and about five per cent in semi-urban areas, the latter defined as having a population of 50,000 to 500,000.
"Social support was a major factor," said lead author Dr. Simone Vigod, a psychiatrist at Women's College Hospital in Toronto. "So women in large urban areas were reporting much lower levels of social support than women in all three other groups."
Many large cities, such as Vancouver, Toronto and Montreal, also have a higher percentage of women who have immigrated to the country compared with rural- and small-town Canada, Vigod said.
"And those women in particular in our study appeared to be at increased risk of having high levels of postpartum depression symptoms," she said.
"It was found to be happening independently of poor social support, although there is a potential that they may be related," explained Vigod, adding that women who have immigrated to Canada, but whose families live elsewhere, may not have the same kinds of support.
There may also be cultural or other barriers to getting help from health professionals who could treat postpartum depression — or even prevent it, by identifying women with an elevated risk for the condition.
Programs aimed at helping new mothers, such as having a nurse make a home visit in the days after the birth, may not be appropriate for all cultures, she said.
"Perhaps there are communities in which that's not as acceptable, for whatever reason. And perhaps a peer member of the community might be a more acceptable alternative.
"We can't necessarily give them mothers and friends and sisters that aren't there, but can we look at other ways of increasing support? There's evidence that peer support can reduce postpartum depression."
Most new mothers experience mood disruptions linked to poor sleep and hormonal changes. But symptoms of postpartum depression go beyond those reactions to include: loss of appetite; insomnia; intense irritability and anger; lack of joy in life; feelings of guilt or inadequacy; difficulty bonding with the baby; and suicidal thoughts, the Mayo Clinic says on its website.
Untreated, postpartum depression may last for many months or even longer.
In rare cases, a new mother can develop postpartum psychosis, which typically occurs within the first two weeks after delivery. The woman may experience confusion and disorientation; hallucinations and delusions; and paranoia. The psychosis may cause her to harm herself or her infant.
Monday's study has particular resonance because of the recent death of Lisa Gibson, whose body was pulled July 27 from the Red River in Winnipeg — three days after her two-year-old daughter Anna and two-month-old son Nicholas were found unresponsive in the bathtub of the family home. They were pronounced dead at hospital.
There is speculation the 32-year-old may have been suffering from severe postpartum depression.
While Winnipeg police have said it may appear Gibson killed her children, they are not ruling out the possibility that someone else was responsible and are still investigating.
Meanwhile, there have been calls for an inquest to examine what kind of health care Gibson may have received following the birth of her son.
Vigod said Canada has "good pathways of care" for trying to identify women with postpartum depression, which she said in many cases can be prevented and is a treatable illness.
"But clearly the results of the study suggest that we can do better."
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