LOS ANGELES — 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 multivehicle accident that was bad enough to send them to hospital emergency rooms were 42 percent higher than they were in the three years before they became pregnant, according to a report published Monday in CMAJ, the Canadian Medical Association Journal.
However, by the third trimester, the risk was significantly lower than it was before pregnancy, and it fell even further in the first year after the women gave birth.
“It amounts to about a 1 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 don’t change their behavior to account for the significant physiological changes in their bodies.
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 6,922 crashes, which worked out to about 4.55 crashes per 1,000 women per year. That was more than double the populationwide average.
During the first month of the first trimester of pregnancy, the crash rate fell slightly to 4.33 crashes per 1,000 women, the researchers found. However, that difference was too small for the drop to be considered statistically significant.
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 1,000 women per year, according to the study. That was the most dangerous month for pregnant women behind the wheel.
Women from all walks of life became more vulnerable during this period, the researchers found. The safest month for all women turned out to be the last month of pregnancy.
The statistics probably underestimate the true risk of driving while pregnant, the report’s authors wrote.
“The message here is not to stop driving,” Redelmeier said. “The message is to start driving more carefully.”