Married women suffer less partner abuse, substance abuse or post-partum depression around the time of pregnancy than women who do not have a partner, according to a University of Toronto researcher.

“What is new in this study is that for the first time we looked at the duration of unmarried cohabitation and found the shorter the cohabitation, the more likely women were to suffer intimate-partner violence, substance abuse or post-partum depression around the time of conception, pregnancy and delivery,” Prof. Marcelo Urquia said on the university's site Friday.

“We did not see that pattern among married women, who experienced less psychosocial problems regardless of the length of time they lived together with their spouses.”

Because more children are being born to unmarried parents, Urquia wanted to delve deeper into the risks and benefits associated with various kinds of relationships.

His study found that unmarried women who lived with their partners for fewer than two years were more likely to experience at least one of the three problems; however, these problems became less frequent the longer the couple lived together.

The problems were most common among women who were separated or divorced, especially if the couple parted less than 12 months before their child was born.

Urquia said it was unclear whether problems such as partner or substance abuse were the cause or result of separations.