A comprehensive program to improve safety for pregnant women and fetuses in motor vehicle crashes: A preliminary report

OBJECTIVE: A program was developed to study the mechanisms of abruptio plac entae and pregnancy loss caused by motor vehicle crashes. The results were intended to be used to develop strategies to improve protection of the fetu s in this setting. STUDY DESIGN: Four integrated projects were conducted: (1) seated anthropom etric measurements and belt fit determination during pregnancy, (2) develop ment of new models of traumatic abruptio placentae, (3) investigations of c rashes involving pregnant women, and (4) the development of the second-gene ration pregnant crash dummy from these data and others. RESULTS: Twenty-two different pregnant subjects in five different height gr oups underwent serial measurements of abdominal surface contours, seat belt fit, and distances between the subjects and various landmarks in the autom obile interior with a laboratory-designed "automobile seat" (seating buck). The abdomen was significantly closer to the steering wheel in the shorter stature group than among the taller women. Beginning at approximately 20 we eks' gestation the fundus of the uterus was above the lower rim of the stee ring wheel. Lap belts fit properly over the anterior superior iliac spine t hroughout gestation, but the lap belt overlapped the uterus in the midsagit tal plane. Two separate mechanisms for traumatic abruptio placentae were te sted: shear failure and tensile failure. In the shear failure model large c ircumferential strains in the uterine wall induce a shear strain across the uteroplacental interface, and the model predicts placental separation at a mean circumferential strain of -58% +/- 8%. By means of finite-element mod eling, it was demonstrated that tensile failure might also be a mechanism t hat causes abruptio placentae during rapid deceleration of the uterus. Cras h investigations were performed in 43 cases involving pregnant women beyond 20 weeks' gestation. There were a total of 8 fetal losses and 8 major comp lications (fetal survival with abruptio placentae, direct fetal injury, or preterm delivery before 34 weeks' as a result of the accident). The best pr edictors of fetal loss or adverse outcome were impact severity and proper s eat belt use. With these newly acquired data a second-generation crash dumm y, known as the Maternal Anthropomorphic Measurement Apparatus version 2b ( MAMA-2b), is being developed. It incorporates strain gauges in the fundal r egion of the fluid-filled uterus plus pressure transducers in both the ante rior and posterior uterus. Criteria are being developed to associate the li kelihood of abruptio placentae with measurements from these instruments tha t correspond to the two major hypothesized mechanisms of abruptio placentae . CONCLUSION: An improved understanding of the elements of automobile crashes that cause fetal loss and other major pregnancy complications has been gai ned through this series of investigations.