Pregnancy and the risk of a traffic crash

Donald A. Redelmeier; Sharon C. May; Deva Thiruchelvam; Jon F. Barrett

doi:10.1503/cmaj.131650

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Unmerited conclusions
Katherine Darbyshire

Posted on: 08 August 2014
Pregnancy and the risk of a traffic crash: considering surveillance bias
Sarah Buchan

Posted on: 21 May 2014
Statistics are Fun but Potentially Misleading
Jeffrey M. McKillop

Posted on: 15 May 2014

Posted on: (8 August 2014)

Unmerited conclusions
Katherine Darbyshire, Family Physician
I was disconcerted (and by that I mean, rather angry) by the conclusion of the article "Pregnancy and the risk of a traffic crash", in the July 8 issue. The first assertion claims that the "study suggests that serious motor vehicle crashes [MVC's] are COMMON [emphasis mine] during the second trimester".It may have been supposed to say, compared with non-pregnancy, or with other trimesters, but as stated this is certainly...
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I was disconcerted (and by that I mean, rather angry) by the conclusion of the article "Pregnancy and the risk of a traffic crash", in the July 8 issue. The first assertion claims that the "study suggests that serious motor vehicle crashes [MVC's] are COMMON [emphasis mine] during the second trimester".It may have been supposed to say, compared with non-pregnancy, or with other trimesters, but as stated this is certainly NOT shown by this study, nor is it endorsed by an informal survey of colleagues, or my own 30 yrs of practice. The authors go on to suggest that pregnant women should be advised to drive safely : condescending toward both pregnant women and their caregivers, to a degree breathtaking to this feminist heart. I do not know if there is a role for caregivers to advise ALL patients to drive safely, but I, for one, do not intend to single out my pregnant patients to remind them of the rules of the road and the ways in which they might be better drivers.
K.Darbyshire, MD, FCFPC
Conflict of Interest:
None
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Competing Interests: None declared.
Posted on: (21 May 2014)

Pregnancy and the risk of a traffic crash: considering surveillance bias
Sarah Buchan, PhD Student
Other Contributors:
Redelmeier and colleagues bring to attention an important issue regarding an increased risk of serious motor vehicle accidents in pregnancy. The authors define their outcome as a crash that resulted in a visit to an emergency department, identified using ICD codes related to vehicle crashes. This article was read with keen interest, considering its implications for safety in pregnancy. However, unmasking bias (also refer...
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Redelmeier and colleagues bring to attention an important issue regarding an increased risk of serious motor vehicle accidents in pregnancy. The authors define their outcome as a crash that resulted in a visit to an emergency department, identified using ICD codes related to vehicle crashes. This article was read with keen interest, considering its implications for safety in pregnancy. However, unmasking bias (also referred to as surveillance bias) (1) should be considered due to its potential contribution to the observed effect. Sackett explains unmasking (detection signal) bias, in that "an innocent exposure may become suspect if, rather than causing a disease, it causes a sign or symptom which precipitates a search for the disease" (2). Given the potential adverse outcomes of trauma during pregnancy (3), women may be more likely to be transported to hospital or hospitalized following a collision, regardless of their injury severity, than non-pregnant women (4). The authors' finding that pregnant women were less likely to be admitted to the hospital than at baseline may suggest that women are visiting the ER out of caution for less severe injuries that may or may not require admission. In this study, pregnant women were more likely than at baseline to attend the ER following motor vehicle collision even as passengers, further supporting this notion.
Sarah Buchan, MSc, PhD Student, Dalla Lana School of Public Health
Ariel Pulver, MSc, PhD Student, Dalla Lana School of Public Health
Joel G Ray, MD MSc, St. Michael's Hospital
1. Haut ER and Pronovost PJ. Surveillance bias in outcomes reporting. JAMA. 2011;305(23):2462-2463.
2. Sackett DL. Bias in analytic research. J Chronic Dis. 1979;32(1- 2):51-63.
3. Vivian-Taylor J, Roberts CL, Chen JS and Ford JB. Motor vehicle accidents during pregnancy: a population-based study. BJOG. 2012;119(4):499-503.
4. Weiss HB and Strotmeyer S. Characteristics of pregnant women in motor vehicle crashes. Inj Prev. 2002;8(3):207-210.
Conflict of Interest:
Dr. Ray had a chance to review this interesting manuscript prior to its submission to CMAJ
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Competing Interests: None declared.
Posted on: (15 May 2014)

Statistics are Fun but Potentially Misleading
Jeffrey M. McKillop
I read with great interest Redelmeier,May,Thiruchelvam, and Barrett's (2014) article on pregnancy and risk of a potential motor vehicle accident. These authors suggest that risk for a motor vehicle accident increases at the beginning of the second trimester of pregnancy and then subsides to baseline by the third trimester. The assumption underneath this risk is that potential cognitive deficits and/or fatigue associated...
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I read with great interest Redelmeier,May,Thiruchelvam, and Barrett's (2014) article on pregnancy and risk of a potential motor vehicle accident. These authors suggest that risk for a motor vehicle accident increases at the beginning of the second trimester of pregnancy and then subsides to baseline by the third trimester. The assumption underneath this risk is that potential cognitive deficits and/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 noted factor in motor vehicle accidents with winter months accounting for a higher frequency of collisions. Similarly, the frequency of birth by month shows a trend toward greater number of births in early and late summer. Counting backwards, on average, most women will enter their second trimester during those months with the most adverse weather conditions, specifically January through March. When the accident occurred (that is which month) may be as, in not more, important then stage of pregnancy.
Conflict of Interest:
None declared
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Competing Interests: None declared.