Women in their second trimester of pregnancy are at much greater risk of a serious motor vehicle crash than they were before their pregnancy, say Canadian doctors who want obstetricians to remind patients about road safety.

In Monday's issue of the Canadian Medical Association Journal, researchers crunched data on emergency department visits for more than 507,000 women who gave birth in Ontario over five years.


Pregnancy is associated with a substantially higher risk of a serious motor vehicle crash during the second trimester, researchers say. (Regis Duvignau/Reuters)

"Our main finding was that the middle months of pregnancy were associated with about a 42 per cent increase in the risk of a life-threatening motor vehicle crash," Dr. Donald Redelmeier, the study's lead investigator and a senior scientist at Toronto's Institute for Clinical Evaluative Sciences, said in an interview.

Redelmeier is concerned that pregnant women might let down their guard on the road during the second trimester when the fatigue, back pain, and insomnia that many face are beginning to take their toll on top of the stress of preparing for the baby's arrival.

"I look after these patients in clinic and they frequently ask me about roller-coasters and airline flights and hot tubs and yet they almost never ask about road safety, despite it being a much larger risk to the safety of Canadians," he said.

The researchers don't advise women to give up driving during pregnancy or to ask their husbands to chauffeur. They simply want women to drive more carefully.

Standard advice applies:

  • Buckle up.
  • Obey traffic signs.
  • Follow the speed limit.
  • Minimize distractions like cellphones.

The risk during the middle months of pregnancy were about 6.47 crash events per 1,000 individuals in a year compared with about 4.55 beforehand. The elevated risk during the second trimester is about the same as for a patient with sleep apnea, Redelmeier said. In comparison, a teenage boy's risk ranks about 10.

Why is 2nd trimester riskier?

Study co-author Dr. Jon Barrett, chief of maternal fetal medicine at Sunnybrook Health Sciences Centre in Toronto, said he was surprised at the magnitude of the effect.

"The first trimester is up to 12 weeks. People might be nauseous but they're still sleeping. The big pregnancy hasn't really taken effect," Barrett said.

Julanna Vine of Toronto has two sons and is expecting her third child in September.

"It does make you think about potentially the fact that I am at a higher risk for getting in an accident, so I will be thinking about that all the time now," Vine said of the findings.

Barrett said driving is one of the behaviours that health-care professionals should bring up with their pregnant patients.

"In the third trimester, maybe they're stopping work, maybe they're so tired and so uncomfortable they're not doing so much activity finally. It's the second  trimester where you still have all these pregnancy symptoms … people are expecting them to function as normal because you know in our society we don't give pregnant women much leeway," Barrett said.

The study was funded by a Canada Research Chair in Medical Decision Sciences, the Canadians Institutes of Heath Research, a community health course at the University of Toronto and the D+H SRI Summer Student Research Program.

With files from CBC's Melanie Glanz