Pregnancy or fetal safety is likely to become an important issue in efforts to reduce traffic accident fatalities. Connolly et al reported that 6–7% of pregnant women undergo some type of traumatic injury during pregnancy and that about two-thirds of such injuries occur during traffic accidents. Klinich et al also reported that about 130,000 women during late-term pregnancy are involved annually in traffic accidents in the United States and that the annual estimate of abortions or stillbirths ranges from 300–3800. The authors previously analyzed the relationship between the severity of injuries sustained by pregnant women and fetal outcomes using data from Japanese automobile insurance claims and associated accidents, as well as from injuries to pregnant women relative to claims for their fetuses. On the basis of these findings, most claims (46%) were submitted by women who were driving automobiles. However, the results of those studies indicated difficulties with predicting adverse fetal outcomes based on injury severity to the mother after a slight (low-velocity frontal or rear) impact, which is the most frequent type of vehicle accident worldwide. Furthermore, injury severity scores did not significantly differ between pregnant occupants with subsequent spontaneous abortion and those whose pregnancies were uneventful, although the scores were significantly higher among pregnant occupants whose fetuses died, including stillbirth and the death of newborn within 1 month of delivery. Therefore, the injury mechanisms to pregnant women and fetuses should be analyzed under the various circumstances experienced by pregnant women during not only high-impact but also low-impact collisions.

Wearing seat belts reduces both the mortality and injury severity of vehicle occupants. According to previous reports, seat belt use during pregnancy improves fetal outcome after motor vehicle accidents. Therefore, seat belt use by drivers and front seat passengers is legally required in many countries. However, some countries exempt pregnant women from mandatory seat belt use. Thus, pregnant occupants of vehicles might not be wearing seat belts at the time of vehicle accidents and subsequently suffer adverse fetal outcomes. Duma et al and Moorcroft et al assessed the amount of stress exerted on the abdomen of pregnant women using finite element (FE) model simulation. They analyzed injury mechanisms under various delta-V (overall accumulative change in velocity) values experienced by pregnant women during collisions and measured strain at the uterus placenta interface (UPI) during impact as a possible predictor of the adverse fetal outcome using the FE uterus model. Their studies used a numeric model, but their assessments included the simplified interior buck model, which does not represent the detailed contour and features of interior components, such as seat shape and stiffness, the steering wheel, instrument panel, or other components that presumably affect the overall kinematics of the occupant. No other studies have comprehensively examined the responses of pregnant drivers during low-speed impact, especially when not wearing a seat belt. Therefore, neither detailed kinematics of pregnant women involved in vehicle collisions nor the biomechanical effects of seat belts on pregnant women under such circumstances are fully understood. The authors, therefore, conducted a series of sled tests to examine the effect of vehicular impact on an anthropomorphic dummy of a pregnant woman. The seated posture of the dummy was based on seat adjustments made by pregnant Japanese volunteers in an actual passenger vehicle. The mechanisms of injury to pregnant drivers and appropriate predictors of adverse fetal outcome are discussed based on the results.