Previously the correlation between the fetal outcome and the injury severity of the pregnant women in automotive collisions were addressed by the authors using the data of the insurance refunds in Japan. The study showed that injury severity scores did not differ significantly between the pregnant occupants with spontaneous abortion and with healthy newborn although the scores were significantly higher in the pregnant occupants whose neonate died. The authors have indicated the prediction of negative fetal outcome with anatomical injury severity of the mothers. Therefore in this study, the abdominal pressure of the pregnant occupant during collisions was focused as a possible predictor of fetal outcome. A series of sled experiment was conducted using the pregnant dummy which represents the anthropometry of the pregnant woman with the gestational age of 30 weeks. The MAMA-2B "Maternal Anthropometric Measurement Apparatus, version 2B" pregnant dummy based on the Hybrid-3 AF5th percentile dummy developed by First Technology Safety Systems Inc. and UMTRI (University of Michigan Transportation Research Institute) was used for the experiments. The values of the pressure during rear impact in a passenger vehicle were measured and compared. The seating posture of the dummy in the experiments was determined by the measurement of pregnant volunteers in an actual passenger vehicle. From the results of the experiments the dominant factor of the change of the abdominal pressure was discussed.