I read with great interest Redelmeier and colleagues’1 article on pregnancy and the risk of a traffic crash. The authors1 suggest that risk for a motor vehicle crash increases at the beginning of the second trimester of pregnancy and then subsides to baseline by the third trimester. The underlying assumption is that potential cognitive deficits or fatigue associated with the second trimester of pregnancy may account for this increased risk. However, a more obvious variable may account for these results. Adverse weather is a known factor in motor vehicle crashes, and crashes occur more frequently in the winter months. Similarly, the frequency of birth by month shows a trend toward a greater number of births in early and late summer. Counting backward, on average, most women will enter their second trimester during the winter months with the most adverse weather conditions, specifically January through March. In which month a crash occurs may be as, if not more, important than the stage of pregnancy.
