Pregnant women are usually concerned about safeguarding their health, but they may be unaware of one of the biggest risks to their well-being: auto accidents.

Researchers recently reported that the chances of being in a wreck go up dramatically for female drivers in the second trimester of pregnancy. At that stage of pregnancy, a woman’s chances of an accident are 42 percent greater than they were during the three years before she became pregnant, the Los Angeles Times says in an article about the study.

On July 13, a chain reaction collision in Tamarac sent a 28-year-old pregnant woman to the Broward Health Medical Center in critical condition. The woman was a passenger in a car that was rear-ended by another car, pushing into her vehicle into a third vehicle, according to the Sun Sentinel newspaper.

In April, an expectant woman and her unborn child died in a car accident in Pensacola after the woman’s sister lost control of the car she was driving and struck a pole and overturned several times, according to Pensacola police. The woman underwent an emergency caesarian section, but neither she nor her baby survived.

Researchers from the University of Toronto identified more than 500,000 women who gave birth in Ontario from 2006 and 2011. They then looked at medical records to see how often the women had gotten into serious wrecks during the three years before they became pregnant, during each trimester of pregnancy, and during the first year after giving birth.

Researchers found that there were around 4.55 accidents per 1,000 women in the three years before they became pregnant. That rate fell to 4.33 crashes per 1,000 women during the first trimester of pregnancy.

However, during the first month of the next trimester, the crash rate increased significantly to 7.66 accidents per 1,000 women. Overall, the accident rate was 6.47 crashes per 1,000 women for the second trimester.

The risk rose in the second semester for all women, regardless of age, income or other factors. The researchers speculated that perhaps fatigue, nausea or other common physiological issues were responsible for increased accidents.

The safest month for pregnant drivers was their last. The women in the study had only 2.74 accidents per 1,000 women in the final weeks of pregnancy. In addition, during the first year after giving birth, the car crash rate fell to 2.35 accidents per 1,000 women.

The average woman has a 1 in 50 statistical risk of a car wreck at some point during her pregnancy, said Dr. Donald Redelmeier of the University of Toronto, who led the study.

Car accidents are the leading cause of fetal death related to a trauma, according to health experts. Dr. Redelmeier said that he’s had pregnant women ask him about the hazards of flying in planes and using hot tubs and rollerblades, but no one has asked about road safety.

“The message here is not to stop driving,” he told the newspaper. “The message is to start driving more carefully.”