Vehicular Obstetrics


Here I am in New Zealand, land of narrow roads, one lane bridges, and at least for us North Americans, the necessity of switching our cultural allegiance from the right to the left hand side of the road. Personally, my greatest struggle is remembering to get into the car through the correct door. Everything seems mirror-imaged, including the controls on the dashboard –you can tell tourists at a crossroad because their windshield wipers start up before their turning signal.

But of course, that’s what I love about the country; I drive a lot when I come here, so traffic always is in my mind, if not in my heart. The ever-distracting scenery seems to require more attention than back home, despite the smaller population .

It all reminds me of a Canadian study reported in the Canadian Medical Association Journal (CMAJ) of July 8/14  http://www.cmaj.ca/content/186/10/742.full  which  ‘compared the risk of a serious motor vehicle crash during the second trimester to the baseline risk before pregnancy.’  It was a large study which used the women themselves as their own controls before and during pregnancy. Interestingly, the relative risk of motor vehicle accidents rose by 42% in the second trimester of pregnancy. As the authors state: ‘The increased risk extended to diverse populations, varied obstetrical cases and different crash characteristics. The increased risk was largest in the early second trimester and compensated for by the third trimester. No similar increase was observed in crashes as passengers or pedestrians, cases of intentional injury or inadvertent falls, or self-reported risky behaviours.’

In other words, there seems to be something, not so much about pregnancy per se, as about the second trimester. It’s obviously only one study and more research has to be done to substantiate the findings, but there is some corroboration mentioned in a Commentary on the report in the same issue: ‘A population-based study from North Carolina found that the highest risk of a motor vehicle crash during pregnancy occurred at 20–31 weeks’ gestation, with a marked decline in the risk of a crash thereafter,3 which is similar to the current study’s results.’  http://www.cmaj.ca/content/186/10/733.full

Pregnancy has long been coloured by reports of altered memory, concentration, sleep deprivation and fatigue, but why does the second trimester seem to be the time of greatest risk? The authors recognized the difficulties and used an interesting set of criteria to help explain it: ‘with all observational studies, it is difficult to make causal inferences. In this article, we assess the associations shown in the study in light of the criteria proposed by Hill:2 temporality, consistency, biological plausibility and evidence of a dose–response effect.’ In other words, do the study findings satisfy these conditions? By and large, they feel they did, with reservations you can address through the links.

As an obstetrician of many years, I can’t remember being asked about the act of driving while pregnant. About being more careful, yes; about where to position the seatbelt, yes; and even about whether or not to report to the hospital if there is a relatively minor accident –more of a bump than a crash. If asked, I’m sure I would have pointed out the altered anatomy and how it might not fit as comfortably behind a steering wheel as pregnancy advanced, but I don’t think I would have singled out the second trimester as being the time of greatest concern. So I’m intrigued by the findings.

The authors have been diligent in pointing out the limitations of their study –such things as distance travelled, frequency of travel, and that after an accident, a pregnant woman might be more likely to report to a hospital because of worry about her foetus even if she weren’t injured herself. It still doesn’t explain the seeming preponderance of risk in the second trimester, however.

I shall certainly be watching for any further analysis of the data, or any follow-up studies this engenders. And with my now heightened curiosity piqued, I may even include a warning to my pregnant patients to be extra careful behind the wheel. I’ll  certainly be more careful if I see one of them get into a car…

 

 

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