The statistical analysis of more than 500,000 pregnant Canadian women found they were significantly more like to get into a serious crash during their second trimester of pregnancy than in the three years before they got pregnant.
"Pregnancy causes diverse physiologic and lifestyle changes that may contribute to increased driving and driving error," wrote the authors, led by Donald Redelmeier of the University of Toronto and published by the Canadian medical association.
According to the study, women in their second trimester -- from four to six months pregnant -- had 42 percent more serious accidents, resulting in hospitalization, than non-pregnant women.
That risk dropped considerably in the third trimester, the last before full-term delivery, when women were about half as likely as non-pregnant women to be driving during serious accidents.
"Our study suggests that serious motor vehicle crashes are common during the second trimester," the others wrote, noting that car crashes are "the leading cause of fetal death related to maternal trauma."