A Computational Model of the Pregnant Occupant: Effects of Restraint Usage and Occupant Position on Fetal Injury Risk

Automobile crashes are the largest single cause of death for pregnant women and the leading cause of traumatic fetal injury mortality in the United States. The purpose of this paper is to present a validated model of a 30 week pregnant occupant and to examine the risk of fetal injury in frontal crashes. The pregnant uterine model was imported into MADYMO 6.0 and included in the 5th percentile female human body model using membrane elements to serve as ligaments and facet surfaces for the overlying skin. A simulation matrix of 17 tests was developed to predict fetal outcome and included frontal crash impulses from minor ( 48 kph) crashes for the driver and passenger occupant positions. The test matrix also included various restraint combinations: no restraint, lap belt, 3-point belt, 3-point with airbag, and airbag only. Overall, the highest risk for fetal death was seen in higher speed frontal accidents in the driver position for all restraint conditions. The peak uterine strain was reduced by 26% to 54% for the passenger position versus the driver position. This difference was due primarily to driver interaction with the steering wheel. For all impact directions, the maternal injury indices were greatest for the unrestrained occupant. In addition, the possibility of direct fetal brain injury from inertial loading alone appears possible and a component that should be included in future models. The current modeling effort has verified previous experimental findings regarding the importance of proper restraint use for the pregnant occupant.