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 study 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.

The research team from the University of Toronto 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 population-wide average of roughly 2 crashes per 1,000 people per year. However, the researchers noted that the women in the study were relatively young, which helps explain the higher crash rate.