(USATODAY.com) - Pregnant women worry plenty, but maybe they should worry more about how they drive: A new study suggests women have more car crashes when they are expecting than they do in the years before or afterward.
The extra risk is concentrated in the second trimester, a time when women are feeling most of the effects of pregnancy but may not drive as carefully as they do with a late-term pregnancy belly, say the authors of the first-of-its-kind study published Monday in the Canadian Medical Association Journal.
One of the authors places the blame partly on so-called "pregnancy brain" – the foggy thinking many women report as pregnancy progresses.
"A normal pregnancy is associated with fatigue, nausea, insomnia, anxiety and distraction," says Donald Redelmeier, a researcher with the Institute for Clinical Evaluative Sciences, Toronto. "All those changes could contribute to driver error."
Redelmeier and colleagues looked at records for more than 500,000 women who gave birth in Ontario. The women were tracked for four years before and one year after the births. The researchers counted each car crash that was serious enough for a woman to show up in an emergency room.
Before pregnancy, the number of such serious crashes for all the women, as drivers, was 177 per month, an annual rate of 4.5 per 1,000. That stayed steady in the first month of pregnancy. By the fourth month, the same women were having 299 serious crashes a month, or an annual rate of 7.6 per 1,000. The rate fell sharply by the last month of pregnancy, to 2.7 per 1,000 – and stayed low the year after the births.
That's probably because new moms drove less or had babies on board when they did, Redelmeier says.
The researchers found no increase in emergency visits for pregnant passengers or pedestrians.
"We are not saying that pregnant women shouldn't drive," Redelmeier says. And they certainly shouldn't leave the driving to male partners – who, as mostly young men, have worse crash rates than women, pregnant or not, he says.
Instead, he says, women should drive as carefully in mid-pregnancy as they apparently do when they have big bellies or infants in the car. "Just slow down and follow the rules of the road," he says.
The study is "robust" and "the results make sense," says Anthony Vintzileos, chief of obstetrics and gynecology at Winthrop-University Hospital, in Mineola, N.Y. Vintzileos, who was not involved in the study, says sleep disorders during pregnancy may play an under-appreciated role in such car accidents.
Sampson Davis, an emergency physician at Meadowlands Hospital Medical Center, Secaucus, N.J., says he's not convinced that the study proves a link between pregnancy symptoms and accidents. The researchers did not account for possible contributing factors such as weather, time of day and other medical conditions, he says. It's odd, he adds, that risk did not increase in the first trimester – when many women, nauseated and tired, feel their worst.
It is is important for pregnant drivers to take care, Davis says: "The farther along the pregnancy is, the more the fetus is exposed…There are no bones around the uterus."
The American College of Obstetricians and Gynecologists urges pregnant women to always buckle up with a lap and shoulder belt and to keep air bags turned on. Pregnant drivers should try to keep 10 inches between the steering wheel and their breastbones, the doctors say.
Pregnant passengers should move front seats back as far as possible or sit in back seats, says the National Highway Traffic Safety Administration.