A pregnant woman who wears a seat belt greatly reduces the risk that her baby will die or be seriously hurt in a vehicle crash, according to a study that debunks the notion that seat belts are harmful to the fetus. “Seat belts absolutely protect the fetus — and not wearing a belt is a big problem," Dr. Mark Pearlman, who led the study, said. "Every single time they get in a motor vehicle, pregnant women should wear their seat belts without question — every single time." In the study, 72 percent of the women were wearing seat belts. Only 38 percent of the women whose babies died or suffered serious complications were wearing seat belts.