Why car crashes are an overlooked threat during pregnancy

Why car crashes are an overlooked threat during pregnancy

Expectant parents often ask their doctors about air travel, hot tubs, and which foods to avoid. They rarely ask about the activity they do almost every day. Driving and riding in a car turns out to be one of the larger physical risks a pregnancy faces, and the research suggests the danger does not behave the way most people would guess.

In the United States, motor vehicle crashes are the leading cause of trauma-related fetal death. One large study put the odds of a serious crash at roughly 1 in 50 over the course of a pregnancy. Below, Davis, Saperstein & Salomon, P.C. looks at how often these crashes happen, when the risk appears to peak, and what the medical evidence says about lowering it.

How often crashes happen during pregnancy

A 2011 review in the American Journal of Lifestyle Medicine by epidemiologists Catherine Vladutiu and Harold Weiss estimated that about 92,500 pregnant women are injured in motor vehicle crashes each year in the United States. The same review described crashes as the leading cause of traumatic fetal death and a top cause of injury-related hospitalization among pregnant women. State-level studies it cited found crash rates among pregnant drivers ranging from roughly 1% to nearly 3%, depending on the state and the years measured.

Measuring the toll on the pregnancies themselves is harder, in part because fetal death certificates do not record whether the mother had recently been in a crash. The best current synthesis comes from a 2020 systematic review in BMJ Open, which pooled 19 studies covering more than 3.2 million women. Among women involved in a crash during pregnancy, it found fetal death or stillbirth in about 6.6 per 1,000 and maternal death in about 3.6 per 1,000. The authors cautioned that the underlying studies varied widely, which is part of why a precise national count of crash-related fetal losses remains out of reach.

The risk peaks in the middle of pregnancy, not the end

The clearest evidence on crash risk comes from a 2014 study in the Canadian Medical Association Journal. A team led by Dr. Donald Redelmeier followed 507,262 women who gave birth in Ontario between 2006 and 2011, comparing each woman against her own record, her crash rate before pregnancy versus during it. Measuring each woman against herself strips out the personal driving habits that complicate most comparisons.

In the three years before pregnancy, these women averaged 177 serious crashes a month as drivers. During the second trimester, the figure climbed to 252 a month. That works out to a 42% jump, with a confidence interval of 32% to 53%. The pattern held regardless of the women's age, income, or education, and across all four seasons.

Two details make the finding more persuasive. The increase showed up only when the women were driving, not when they rode as passengers or walked as pedestrians, which points to something about being behind the wheel rather than simply spending more time near traffic. And the elevated risk faded in the third trimester, then dropped below baseline in the year after birth. Redelmeier and his colleagues pointed to the fatigue, insomnia, nausea, and distraction common in mid-pregnancy, which arrive once the careful early months have passed, as a plausible explanation.

What a crash can do to a pregnancy

Most pregnant patients admitted to a hospital after a crash have relatively minor injuries, and the baby's outcome usually follows the mother's: When she does well, the baby tends to as well. The serious exceptions, though, can follow even a modest impact. The complications clinicians watch for most closely are:

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• Placental abruption, in which the placenta tears away from the uterine wall. It is the most common cause of crash-related fetal death, and reported rates run from about 1% to 5% in minor crashes to as high as 20% to 50% in severe ones.
• Uterine rupture, which is rare but carries a fetal mortality rate near 100% when it does happen.
• Maternal shock, when heavy blood loss causes the body to divert blood to vital organs and away from the fetus.
• Direct fetal trauma, usually to the head, although the uterus and abdominal wall give the fetus considerable protection.

The same body of evidence points to a range of specific risks: crashes during pregnancy are linked to higher rates of preterm birth, placental abruption, and fetal loss, and even a minor impact can matter. That is why obstetricians urge an evaluation after any crash, including low-speed ones and cases where the mother feels fine.

What the evidence says about driving more safely

One point in the research gets muddled often enough to be worth stating plainly: Seat belts and airbags protect pregnant occupants. Restraints can contribute to injury in a high-speed crash, but going unbelted is far more dangerous. Standard guidance is to run the lap belt low, under the belly and across the hips and pelvic bone, keep the shoulder strap between the breasts, and leave about 10 inches between the breastbone and the steering wheel where the seat allows.

The Ontario researchers were careful to say their findings were not a reason to stop driving. As Redelmeier put it at the time, the message was to drive more carefully, particularly in the months when the data suggests attention tends to slip.

After a crash: medical and legal follow-up

Some fetal injuries cause no symptoms the mother can feel, so doctors generally recommend a medical check after any crash during pregnancy, then watching for warning signs such as abdominal pain, vaginal bleeding, contractions, or a change in the baby's movement. Pediatricians also suggest noting a prenatal crash in a child's records, because some effects of fetal head trauma, including developmental or intellectual delays, may not appear until later in childhood.

The legal picture depends on the state. New Jersey is one example worth noting: The state's Limitation on Lawsuit Threshold, sometimes called the verbal threshold, limits certain claims for injuries that are not permanent, but state law treats the loss of a fetus as a permanent injury, which preserves the right to file. Filing deadlines and the long delay before some developmental injuries surface are among the reasons these cases can grow complicated.

Methodology

This article draws on peer-reviewed research and public health data rather than any original survey. The central figure on crash risk comes from Redelmeier, May, Thiruchelvam, and Barrett, “Pregnancy and the risk of a traffic crash,” a population-based, self-matched cohort study of 507,262 women who gave birth in Ontario between April 1, 2006, and March 31, 2011. The study counted only crashes serious enough to require emergency care and compared each woman's pre-pregnancy rate against her second-trimester rate; the 42% increase carries a 95% confidence interval of 32% to 53% (p < 0.001). Because the cohort included only women who went on to give birth, it leaves out crashes that ended a pregnancy and so likely understates the true risk. The study population is Canadian; the underlying physiology and driving conditions are broadly comparable to those in the U.S., but readers should keep the national source in mind.

U.S. incidence figures (roughly 92,500 injured pregnant women per year, plus the state-level crash rates) come from Vladutiu and Weiss, “Motor vehicle safety during pregnancy.” The fetal and maternal mortality rates following crashes during pregnancy — about 6.6 fetal deaths or stillbirths and 3.6 maternal deaths per 1,000 — are pooled estimates from the systematic review by Amezcua-Prieto and colleagues. which combined 19 studies covering more than 3.2 million women, the large majority in high-income countries. Those pooled rates carry wide confidence intervals and high statistical heterogeneity, which is why the article presents them as approximate rather than precise counts. Injury complications and their rate ranges are also drawn from that review. Percentages for placental abruption and similar complications reflect ranges reported across the clinical literature, not a single dataset.

This story was produced by Davis, Saperstein & Salomon, P.C. and reviewed and distributed by Stacker.