When pregnant women are most at risk of car crashes

car crash
car crash 

Pregnancy is not without health risks, and now researchers from Canada have identified a new one: serious car crashes.

During the second trimester of pregnancy, women's odds of being behind the wheel in a multi-vehicle accident that is bad enough to send them to hospital are 42 per cent higher than in the three years before they became pregnant, according to a study published Monday in the Canadian Medical Association Journal.

However, by the third trimester, the risk is significantly lower than it was before pregnancy. It falls even further in the first year after birth.

Study: The number of car crashes in which a pregnant woman was the driver, in the years proceeding her pregnancy, during ...
Study: The number of car crashes in which a pregnant woman was the driver, in the years proceeding her pregnancy, during the nine months, and in the year after birth. Photo: CMAJ

"It amounts to about a one in 50 statistical risk of the average women having a motor vehicle crash at some point during her pregnancy," said Dr Donald Redelmeier of the University of Toronto, who led the study.

The research team, from the University of Toronto and affiliated institutions, wondered whether the fatigue, distraction, nausea and other annoyances that accompany pregnancy might make women more vulnerable behind the wheel.

They were particularly curious about the second trimester, a time when pregnant women often feel like their normal selves; as a result, they often don't change their behaviour to account for the significant physiological changes in their bodies.

Most dangerous times

The researchers identified more than 500,000 women who gave birth in Ontario from 2006 to 2011. They combed through data from Ontario hospitals to see how often they got into serious car crashes during the three years before they became pregnant, during each trimester of their pregnancy, and for the first year after their babies were born.

The researchers counted 6922 crashes, which worked out to about 4.55 crashes per 1000 women per year. That was more than double the population-wide average of roughly 2 crashes per 1000 people per year. However, the researchers noted that the women in the study were relatively young, which helps explain the higher crash rate.


During the first month of the first trimester of pregnancy, the crash rate fell slightly to 4.33 crashes per 1000 women, the researchers found. 

But something had changed by the first month of the second trimester: during that month, the women's crash rate soared to 7.66 collisions per 1000 women per year, according to the study. That was the most dangerous month for pregnant women behind the wheel.

For the entire second trimester, the crash rate was 6.47 collisions per 1000 women per year, which was 42 per cent higher than during the baseline period.

Women from all walks of life became more vulnerable during this period, and the increased crash risk was seen in all women regardless of age, socioeconomic status, whether their babies were born early, the sex of their babies and most other factors. Time of day, week and year also had no effect. 

The safest month for all women turned out to be the last month of pregnancy: in those final weeks, the women tracked had only 2.74 crashes per 1000 women per year. And in the year after giving birth, the accident rate dropped even more, to 2.35 crashes per 1000 women per year.

The women saw no increase in car accident injuries when they were passengers in other people's cars or as pedestrians, according to the study.

"The message here is not to stop driving," Dr Redelmeier said in a video released by the Sunnybrook Research Institute. "The message is to start driving more carefully."

He added that the pregnant women he cares for ask about the risks of flying planes, soaking in hot tubs and skating on rollerblades, but said that "not once has a woman asked me about road safety despite it being the much larger, greater risk".

- Los Angeles Times