What we do know is that the way hospitals and the National Highway Traffic Safety Administration keep records doesn’t fully capture how many fetuses are killed or injured in car crashes each year.
“There are many reasons pregnancy-related crash statistics are vastly underreported or unaccounted for,” says Hank Weiss, PhD, adjunct associate professor of population health sciences at the University of Wisconsin School of Medicine and Public Health, who has published much in this area.
For example, records of fetal deaths are stored separately from regular death certificates. And NHTSA and the Centers for Disease Control and Prevention only pull regular death certificates when reporting on transport-related incident data. So fetal deaths are not well documented in motor vehicle crash reports. Further, fetal death records are typically not generated if the pregnancy is under 20 weeks.
Also, if the pregnant driver or passenger dies from a crash but there is no delivery or autopsy, the fetal death or its cause may not be reported or even ascertained.
Even when there is a record of a fetal death or injury from the mother’s trauma, it is not classified in hospital or vital statistics data systems with a specific cause. “It basically just says ‘death or injury to the fetus due to maternal injury,’” Weiss says. “They fall through the cracks in numerous ways and this leads to little ongoing reporting of the problem.”
In the absence of firm records, experts instead can only estimate the number of fetal deaths, based largely on annual population pregnancy rates and numbers of car crashes. By extrapolating, the research suggests that car crashes in the U.S. are the leading cause of fetal injury, and that each year some 160 pregnant women are killed in motor-vehicle crashes, and 800 to 3,200 fetuses die when the mother survives.
In addition, Duma estimates that car crashes are responsible for more fetal losses per year than for deaths of children ages zero to 4 who are strapped into car seats. “And yet look at how much we talk about car seats,” he says.
Fetuses are particularly at risk during car crashes in numerous ways: A fetus can be injured from direct force during a crash, as happened to Olsen when she was pregnant. But the most documented cause of harm to the pregnancy in a crash is placental abruption, which is when the placenta detaches from the uterus, depriving the fetus of oxygen. Other pregnancy-related problems include a ruptured uterus, a drop in fetal heart rate, and early delivery. Of course, if the mother dies in a crash, that can lead to the death of the fetus as well.
Perhaps not surprisingly, the higher the speed of the crash, the greater the potential for injury. One study led by Duma involving computer-simulated crashes of cars with pregnant occupants found that the risk of fetal injury was 33.5 percent at speeds of 15 miles per hour and 61 percent at 25 mph.
Despite this high risk, there has been little innovation from car manufacturers aimed at improving seat belts for pregnant people.
General Motors, Ford, Toyota, and Volvo have funded some research in this area or invested in computer models that assess risk to pregnant occupants in crash tests, but there are only a handful of crash-test dummies that simulate a pregnant person. And those models are rudimentary, says Kathleen D. Klinich, PhD, associate research scientist at the University of Michigan Transportation Research Institute, who helped to develop and crash-test one of the first pregnant dummies.
What scientists have found, however, is that the three-point seat belt offers better protection for pregnant people than no seat belt at all. Research led by Klinich, published in the early 2000s (and partially funded by NHTSA and GM), was the first to show that the risk of adverse outcomes for fetuses is reduced when the mother is wearing a seat belt in a car crash.
But does the seat belt as presently designed mitigate that risk enough for pregnant people and their unborn babies? Could more be done? After a flurry of research from the late 1990s to about 2011, there have not been many studies published on this issue, in large part because funding for research that might improve car restraint systems for pregnant people hasn’t been a priority.