OVER the years, pregnant women have asked Donald Redelmeier, at Toronto’s Sunnybrook Hospital, about the dangers of scuba diving, hot tubs, flying, mountaineering, cycling, bear attacks and all sorts of other exotic risks. But they never worry about road accidents. His new study, published in the Canadian Medical Association Journal, suggests they should.

Dr Redelmeier and his colleagues wanted to know if pregnancy makes a woman driver more likely to be involved in a car crash. So they examined data from the Ontario Health Insurance Plan, which records health visits for the Canadian province’s 13m residents. The researchers looked for women who, in the months before giving birth, visited a hospital emergency unit after a car accident in which they had been driving. They then looked at those women’s hospital visits in the three years before becoming pregnant and for one year following the birth.

They found that being pregnant made the women 42% more likely to be in a serious car crash. The risk peaked in the fourth month of pregnancy. It seems that being pregnant is about as dangerous for drivers as having sleep apnoea, which causes people to snore and choke themselves awake throughout the night, leaving them tired during the day.

Women’s driving seemed to be affected regardless of how rich or poor or old they were, whether their pregnancy was complicated or straightforward, or whether they already had children. To rule out the possibility that pregnant women simply had an increased propensity to seek care—or, in layman’s terms, were neurotic—they looked at whether they were more likely to go to hospital when involved in crashes that they did not cause, because they were passengers or pedestrians. They were not.

Dr Redelmeier and his colleagues are raising the uncomfortable possibility that there may be something to the condition known as “baby brain”, the distracted, foggy neurological state which has been observed, anecdotally, in expectant females. Dr Redelmeier argues, gingerly, that mothers-to-be can be tired, nauseated, anxious and distracted by the big event to come. He suggests that reminders about road safety should be part of normal prenatal check-ups.

However, these findings should not be interpreted as a call for young husbands to take over the driving from their pregnant wives. Dr Redelmeier cautions that this would make matters worse. “Men in this age group”, he says, “are even more dangerous behind the wheel.”