Being pregnant significantly increases a woman driver's chances of having a serious car crash, research has shown.

The risk of requiring hospitalisation for injuries sustained in a road accident increases by 42% for pregnant women in the second trimester of pregnancy - weeks 14 to 26. 

Canadian scientists studied more than 500,000 pregnant women and found that about one in 50 can expect to be involved in a car crash while at the wheel. 

In the three years before getting pregnant, the women had an average of 177 crashes between them per month. This rate rose by 42% to 252 crashes per month for those in the second trimester, or middle period of pregnancy. 

Writing in the Canadian Medical Association Journal, the researchers said the 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", he said.

"Even a minor motor vehicle crash during pregnancy could lead to irreparable consequences for mother and child", he added.  

Accidents amongst pregnant pedestrians or car passengers did not see an increase, while pregnancy was found not to increase the rate of falls or risky behaviour. 

The study, published in the Canadian Medical Association Journal, explored whether common features of pregnancy such as nausea, fatigue, insomnia and distraction might contribute to human error and increase the risk of traffic accidents.

Researchers also outlined the effects of "baby brain" - a mental "fog" said to be associated with pregnancy - in their paper, but stop short of linking this directly to a heightened risk of road accidents. 

"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", they wrote. 

The absolute risk of pregnant women having a serious car crash was still found to be lower than that of men of the same age.