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ICES study finds pregnancy is associated with substantial risk of a serious motor vehicle crash during the second trimester


Women in their second trimester of pregnancy are 42 per cent more at risk of a serious motor vehicle crash compared to the same women before pregnancy, say researchers of a study released today by the Institute for Clinical Evaluative Sciences (ICES). The increased risk amounts to an extra 75 crashes sending pregnant motorists to hospital each month in Ontario. Almost all crashes could be prevented by a small change in driver behavior.  

“An effect of this magnitude equals about one crash for every 50 pregnant women,” says Dr. Donald Redelmeier, lead investigator and ICES senior scientist. "Pregnant women often worry about air flights, scuba diving, hot tubs and other topics in maternal health, yet may overlook that traffic crashes are greater health risks,” adds Redelmeier, also a staff physician at Sunnybrook Health Sciences Centre and a senior scientist at Sunnybrook Research Institute.  

Normal pregnancy can cause diverse physiologic changes including fatigue, nausea, distraction, and insomnia. These changes may contribute to driver error and yet road safety is not discussed in prenatal care guidelines say the researchers.  

In the paper, published in the CMAJ, the researchers identified every woman in Ontario who gave birth between April 1, 2006 and March 31, 2011 (a sample size of 507,262 total women). The researchers found:  

  • The second trimester of pregnancy led to a 42 per cent increase in the risk of a serious motor vehicle crash.
  • The increased risk included diverse patient populations, distinct obstetrical cases and different crash characteristics.
  • The absolute risk was about twice the overall population average but still below male drivers at the same age.  

“These findings do not mean pregnant women shouldn’t drive; in fact, men in this age group have higher risks of a motor vehicle crash. These findings are not a reason to decide not to have children or a reason to stop driving. Instead, the findings emphasize the need to drive more carefully. An awareness of the elevated risk during the second trimester of pregnancy does merit consideration for prenatal care,” added Redelmeier.  

The researchers recommend that pregnant women, particularly those in their second trimester, avoid excessive speed, signal when turning, yield right-of-way, obey stop signs, minimize distractions, and always wear a seatbelt. The authors also stress the importance of standard safety practices for all drivers, moreover, because we all share the road with others who might be pregnant.  

The study “Pregnancy and the risk of a traffic crash,” was published today in the CMAJ.

Authors: Donald A. Redelmeier, Sharon C. May, Deva Thiruchelvam and Jon F. Barrett.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.  

For the latest ICES news, follow us on Twitter: @ICESOntario


  • Deborah Creatura
  • Communications, ICES
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