If you're pregnant and still driving, you may want to take extra care on the road.
The Canadian study of more than 500,000 pregnant women found that in the three years before getting pregnant, the women between them had an average 177 crashes per month.
The crash rate rose to 252 per month (up 42%) in the second trimester, or middle period, of pregnancy.
Statistically, about one in 50 pregnant women can expect to be involved in a serious car crash while at the wheel, say the scientists writing in the Canadian Medical Association Journal.
The increased crash rate was "almost fully explained" by multiple-vehicle collisions in which the woman had been driving a car.
Lead researcher Dr Donald Redelmeier, from the University of Toronto, said: "Pregnant women often worry about air flights, scuba diving, hot tubs and other topics in maternal health, yet individuals may overlook traffic crashes despite their greater health risks.
"These findings are not a reason to decide not to have children or a reason to stop driving; instead, the findings primarily emphasise the need to drive more carefully."
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He added: "Even a minor motor vehicle crash during pregnancy could lead to irreparable consequences for mother and child. These findings underscore the importance of prevention and indicate that good prenatal care includes safe driving."
No similar increase in accidents was seen among pregnant pedestrians or car passengers. Nor did pregnancy increase the rate of falls or risky behaviour.
The study, which involved 507,262 pregnant women, looked at whether common features of pregnancy such as nausea, fatigue, insomnia and distraction might contribute to human error and increase the risk of traffic accidents.
In their paper, the researchers mention the effects of "baby brain" - a mental "fog" said to be associated with pregnancy - but stop short of linking it directly to a heightened risk of car accidents.
They wrote: "Subjective disturbances during pregnancy are commonly reported in the obstetrical literature where absentmindedness is denoted as 'baby brain' or other negative terms.
"Community surveys suggest that about half of pregnant women complain of sporadic cognitive lapses; however, laboratory studies in this setting provide results with uncertain clinical relevance."
The researchers also stressed that the absolute risk of pregnant women having a serious car crash was still lower than that of men of the same age.