## 4 Discussion  
By analyzing the kinematics and biomechanical parameters of a pregnant dummy, we examined the safety of a correctly used conventional lap-and-shoulder seatbelt for pregnant rear-seat passengers and further analyzed the safety of a conventional seatbelt equipped with pretensioner and force limiter systems. Because we used a pregnant woman dummy with a similar stature to an average Japanese pregnant woman [9], this reconstruction of a motor vehicle collision involving a pregnant woman sitting in the rear seat had enough reliability. In this context, one previous study performed sled tests using a similar dummy to examine the mechanism of neck injuries, due to shoulder belt compression [27]. However, because neither the interaction between the lap belt and abdomen nor the seatbelt loads were examined, to our knowledge, our study is the first to examine the kinematics of the entire body and its related parameters under the seatbelt conditions used by pregnant passengers. Seatbelt methods that pass the lap belt across the left and right thighs or use the extra restraint device resulted in greater displacements and resultant accelerations of the head, chest, and pelvis than the correct use of the conventional seatbelt. On the basis of these results, we concluded that the correctly used conventional lap-and-shoulder seatbelt provided enough safety. Previous reports suggested that 12.7-27.5% of pregnant women wear seatbelt incorrectly, due to the misunderstandings regarding the correct way to use them [17; 28]. Therefore, healthcare professionals must educate pregnant women about the correct use of conventional rear-seat safety belts, based on current scientific evidence. To improve the safety of pregnant rear-seat passengers, it is important to provide better restraint and reduce the applied external forces. Previously, rear-seat passengers were considered to be safer than front seat passengers. However, the widespread installation of seatbelt safety systems with a pretensioner and force limiter has dramatically improved the safety of front seats. In contrast, the safety of rear seats remains minimally improved [29; 30]. [PERSON] et al. reported that rear-seat passengers suffered more serious chest injuries than drivers or front seat passengers in MVCs, owing to the lack of a pretensioner and force limiter in the rear seat [31]. [PERSON] et al. reported that a pretensioner and force \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{3}{c}{**Test D**} & \multirow{2}{*}{**Test F (FL)**} & \multirow{2}{*}{**Test G (PT + FL)**} & \multirow{2}{*}{**Test G (PT + FL)**} \\  & & **(Conventional & Seatbelt)** & & & \\ \hline Head & Resultant accel. (m/s\({}^{2}\)) & 312.0 & 305.7 & 273.1 & 259.3 \\  & Time (ms) & 76 & 91 & 91 & 96 \\ Neck & Flexion moment (Nm) & 73.1 & 83.5 & 68.2 & 62.8 \\  & Time (ms) & 98 & 99 & 118 & 117 \\  & Extension moment (Nm) & 38.2 & 21.6 & 20.6 & 16.1 \\  & Time (ms) & 62 & 64 & 76 & 79 \\ Chest & Resultant accel. (m/s\({}^{2}\)) & 666.2 & 470.4 & 357.2 & 284.4 \\  & Time (ms) & 64 & 60 & 71 & 66 \\  & Deflection right (mm) & 8.5 & 9.0 & 6.9 & 6.8 \\  & Time (ms) & 106 & 107 & 125 & 104 \\  & Deflection left (mm) & 26.9 & 25.6 & 21.9 & 19.8 \\  & Time (ms) & 69 & 81 & 64 & 91 \\ Pelvis & Resultant accel. (m/s\({}^{2}\)) & 320.4 & 221.6 & 304.4 & 221.8 \\  & Time (ms) & 63 & 62 & 69 & 68 \\ Seatbelt loads & Lap load (kN) & 11.1 & 8.1 & 9.2 & 7.2 \\  & Time (ms) & 61 & 58 & 61 & 59 \\  & Shoulder load (kN) & 9.2 & 7.4 & 3.8 & 3.8 \\  & Time (ms) & 64 & 68 & 75 & 57 \\ \hline \hline \end{tabular} PT: pretensioner, FL: force limiter, accel: acceleration.  
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