Nearly nine in ten fell short, even after instruction
For decades, the seatbelt has stood as one of civilization's most effective lifesaving inventions — yet a new study from the University of British Columbia reveals that its design has quietly excluded one of the most vulnerable groups it was meant to protect. Biomedical engineers found that nearly nine in ten pregnant drivers cannot achieve recommended seatbelt positioning, not through inattention or ignorance, but because the geometry of current restraint systems was never built to accommodate a changing body. The research, conducted with 333 participants and supported by Toyota and Autoliv, marks a reckoning with a long-standing blind spot in automotive safety — and the beginning of an effort to correct it.
- Only 38 of 333 pregnant participants — just 11.4% — could position a seatbelt correctly, even after hands-on instruction, exposing a near-universal failure in restraint design.
- As pregnancy advances, the growing abdomen pushes shoulder belts off-center and causes lap belts to 'nest' into soft tissue beneath the belly, placing organs at greater risk in a crash.
- Researchers identified a fundamental geometric paradox: adjusting the shoulder anchor to help one placement automatically worsens the other, making correct positioning physically impossible with current systems.
- Despite the gap, seatbelts still reduce crash fatalities by 47% and serious injuries by 52% — the goal is better design, not discouraging pregnant occupants from buckling up.
- UBC is now partnering with Autoliv and Toyota to build computer models of pregnant anatomy, aiming to redesign the next generation of restraint systems before more lives are lost to an overlooked flaw.
When a team of biomedical engineers at UBC asked how pregnant bodies fit inside the safety systems cars were built for, the answer was unsettling. Of 333 pregnant participants, only 38 — just 11.4 percent — managed to position a seatbelt the way safety experts recommend. Nearly nine in ten fell short, even after receiving instruction and hands-on guidance.
The stakes are real. Seatbelts work by routing crash forces through the skeleton, keeping soft tissue and organs out of harm's way. The shoulder belt should run between the breasts and down the center of the chest; the lap belt should sit low across the hips. But pregnancy reshapes the body in ways current designs don't accommodate. As the abdomen grows, it pushes the shoulder belt sideways across the breast. The lap belt, meanwhile, can fold into the soft tissue beneath the belly — a phenomenon researchers called 'nesting' — rather than lying flat against it.
Led by Dr. Peter Cripton and conducted under the clinical supervision of Dr. Jason Burrows, the study used 3D body scanning to document these changes across participants ranging from six to 38 weeks pregnant. What emerged was a design paradox: lowering the shoulder anchor helps breast placement but pulls the belt away from the shoulder's center. Raising it does the opposite. With current systems, pregnant occupants cannot achieve both correct positions at once — a structural limitation, not a user error.
Cripton and his team are careful to stress that seatbelts remain essential, reducing crash fatalities by 47 percent and serious injuries by 52 percent. The research, a collaboration with the Toyota Collaborative Safety Research Center, is now moving forward with Autoliv to build computer models of pregnant anatomy and test new restraint designs. As the automotive industry shifts toward virtual testing, this data offers a rare opportunity to design safety systems that finally account for the full range of human bodies — including those carrying new life.
A team of biomedical engineers at UBC set out to answer a practical question: how do pregnant bodies fit inside the safety systems cars were built for? What they found was sobering. Of 333 pregnant participants in their study, only 38 managed to position a seatbelt the way safety experts recommend. That's 11.4 percent. Nearly nine in ten fell short, even after receiving instruction and hands-on guidance on how to wear the belt correctly.
The reason matters. Seatbelts work by channeling crash forces through the body's strongest parts—the skeleton. When positioned correctly, the shoulder belt runs between the breasts and down the center of the chest, while the lap belt sits low across the hips and pelvis, hugging the body snugly. This geometry keeps vulnerable organs and soft tissue out of harm's way. But pregnancy reshapes the body in ways current seatbelt designs don't accommodate. As the abdomen grows, it pushes the shoulder belt sideways, off the center of the chest and across the breast instead. The lap belt, even when positioned correctly, sometimes folded into the soft tissue beneath the belly rather than lying flat against it—a phenomenon the researchers called "nesting," which became more pronounced as pregnancy advanced.
The study, led by Dr. Peter Cripton, a professor in UBC's school of biomedical engineering, used 3D body scanning to document these changes. Researchers recruited participants from the maternity clinic at the Jim Pattison Outpatient Care and Surgery Centre in Surrey, scanning women ranging from six to 38 weeks pregnant, representing a broad spectrum of body types. Under the supervision of Dr. Jason Burrows, an obstetrics and gynecology clinical professor, each participant was shown how to adjust a seatbelt, then scanned while seated in a production vehicle with a standard configuration.
What emerged was a design paradox. The researchers identified a fundamental conflict in seatbelt geometry. Lowering the shoulder anchor point helps position the belt between the breasts, but it pulls the belt away from the center of the shoulder. Raising the anchor improves shoulder placement but moves the belt across the breast. With current systems, pregnant occupants cannot achieve both positions simultaneously. This isn't a matter of user error or lack of instruction. It's a structural limitation of restraint systems designed without pregnant anatomy in mind.
Cripton and his colleagues emphasize that seatbelts remain essential. Worn correctly, they reduce the risk of death in a collision by 47 percent and serious injury by 52 percent. The goal of the research is not to discourage pregnant people from buckling up, but to inform the next generation of vehicle safety design. "Pregnant anatomy introduces a different set of challenges to motor vehicle safety than has previously been considered, yet there is limited data available," Cripton said. The study highlights a broader gap in safety research: human bodies vary widely, and safety models have historically failed to fully account for female anatomy, particularly the anatomy of pregnancy.
The work has caught the attention of the automotive industry. The research was a collaboration between UBC and the Toyota Collaborative Safety Research Center. The team is now partnering with Autoliv, a major manufacturer of restraint systems for Toyota and other automakers, to build computer models of pregnant bodies and test new restraint designs against them. As automakers shift toward virtual testing, there's an opportunity to include varying body sizes, types, and properties in digital human models. The data from this study will inform that development. The findings will be presented at the 10th World Congress of Biomechanics in Vancouver, marking the beginning of what may be a significant shift in how the automotive industry thinks about protecting one of its most vulnerable occupants.
Notable Quotes
Pregnant anatomy introduces a different set of challenges to motor vehicle safety than has previously been considered, yet there is limited data available.— Dr. Peter Cripton, UBC biomedical engineering professor and study lead
The goal of our research is not to question that guidance, but to help inform how future restraint systems are developed and used.— Dr. Peter Cripton
The Hearth Conversation Another angle on the story
Why does this matter so much? Pregnant people are a relatively small percentage of drivers at any given moment.
True, but the study reveals something bigger—that safety systems designed without certain bodies in mind fail those bodies. It's not about the percentage. It's about the principle that engineering should account for human diversity.
But the study says seatbelts still save lives. So what's the actual risk here?
The risk is real but often invisible. A pregnant person wearing a seatbelt incorrectly might feel protected when they're actually more vulnerable. In a crash, forces could hit soft tissue instead of bone. The study doesn't say don't wear seatbelts. It says current designs create a trap where proper positioning is nearly impossible.
If 89 percent of people can't do it right, is the problem the design or the instruction?
The researchers gave instruction. People still couldn't achieve it. That tells you it's not about understanding the guidance—it's that the geometry itself is incompatible with how pregnancy changes the body. You can't position a shoulder belt between breasts and centered on the shoulder simultaneously when pregnancy has shifted both those landmarks.
What does "nesting" mean in practical terms?
Imagine the lap belt folding into the soft tissue of the belly instead of lying flat against the pelvis. In a crash, that belt could compress internal organs rather than distribute force safely through bone. It happens more as pregnancy progresses because there's more tissue for it to nest into.
So what happens next? Do automakers actually change their designs?
That's the open question. The researchers are now working with Autoliv to build computer models and test new designs. But moving from research to production takes years. In the meantime, pregnant people are driving in cars built for bodies that don't match theirs.