RICHMOND, Va. - Shifting the focus from infants and children in safety seats, researchers and automakers are looking to prevent fetal deaths by making car travel safer for expectant mothers.

Biomedical researchers are working with automakers to develop a computer-aided model of pregnant drivers and passengers so they can develop better crash-protection features in vehicle designs.

Stefan Duma, head of the Virginia Tech-Wake Forest University School of Biomedical Engineering and Sciences, said the school recently completed a three-year research project, partly funded by Ford, to gather data about the tissue composition and dimensions of pregnant women and their fetuses.

"We can develop restraint systems for any vehicle and any occupant," Duma said, "but we first have to see the injuries themselves, what happens to the placenta and uterus tissues during an accident."

No official federal statistics are kept on fetal deaths in car accidents. But Duma says various groups estimate that 300 to several thousand such deaths occur annually as a result of vehicle crashes - about four times the number of victims between infancy and age 4.

Overall, about 27,000 occupants died in car crashes in 2008, according to the National Highway Traffic Safety Administration, and auto accidents are the single largest cause of death for pregnant women.

Melissa Schiff, an obstetrician and epidemiologist at the University of Washington's Harborview Injury Prevention and Research Center, welcomes the attention to pregnant women.

"We really do need to get more information and to design vehicles better for this special population," said Schiff, who has done studies on vehicle crashes and pregnancy.

Researchers used data from CT scans taken at Wake Forest's hospital to determine the dimensions of a fetus, uterus, and placenta at 30 weeks' gestation. They also tested varying forces' effects on actual uterine and placental tissue samples so they could devise a more accurate simulation of how crashes affect women and their fetuses.

The majority of fetal deaths occur when the force of a crash tears the placenta from the uterus, cutting off oxygen to the fetus. Duma says pregnant women should make sure to wear their lap and shoulder belts properly and resist the temptation to shift the lap belt higher on the abdomen.