Protecting the Pregnant Occupant: Dynamic Material Properties of the Placenta

Automobile crashes are the largest cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, a useful tool to evaluate the risk of fetal loss in motor vehicle crashes, are limited to quasi-static material properties of the placenta. This study presents a total of 8 dynamic uniaxial tension tests on the full thickness of the placenta and 8 dynamic uniaxial tension tests on the maternal side of the placenta. These tests were completed from 4 human placentas to determine material properties at a strain rate of 6 strains/s. The results show that the average peak strain at failure for both the maternal portion and the full thickness placenta are similar with a value of 0.36. However, the peak stress for the full thickness placenta, 119.4 kPa, is much higher than the peak stress for the placenta with the chorionic plate removed, 27.5 kPa. These results are compared to previous quasistatic data and found to be significantly different (p<0.01). In summary, dynamic loading data for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in motor vehicle crashes. Moreover, for predicting placental abruption, the computational model for the maternal side of the placenta should reflect the material properties for the villus structure of the placenta. INTRODUCTION A utomobile crashes are the largest cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States (US) (Attico et al., 1986; Weiss et al., 2002). Each year in the US, 800 to 2800 fetuses are killed from motor vehicle crashes (Klinich et al., 1999a; Klinich et al., 1999b; Pearlman, 1997; Pearlman et al., 1996; Weiss, 2001). The best way to protect the fetus is to protect the mother considering that maternal death has a near 100% fetal loss rate (Pearlman et al., 1990a). If the mother survives, protection of the fetus may best be accomplished by preventing placental abruption. Placental abruption, which is the premature separation of the placenta from the uterus, has been shown to account for 50% to 70% of fetal losses in motor vehicle crashes (Pearlman et al., 1990b).