The development and testing of new instruments for operative vaginal delivery

OBJECTIVE: Little innovation has occurred in recent years in the instruments available for operative vaginal delivery. The purpose of this study is to develop a technique to test the utility of an investigational device, the obstetric bonnet, and measure the forces it places on the fetal head. STUDY DESIGN: We constructed a model of the fetal head capable of measuring both compression and vacuum created by an applied device. A total of 18 devices were tested to a maximum traction of 60 pounds. RESULTS: A significant linear relationship exists between the traction applied and the compression (R² = 0.42, p = 0.0004) and vacuum (R² = 0.85, p = 0.0001) created. Compression and vacuum recorded at maximum recommended traction were 1.1 lb/sq in and 31 cm Hg, respectively. CONCLUSION: These findings explain the mechanics of this interesting device, and demonstrate forces that compare favorably with those known to occur with forceps or vacuum extraction. (Am J Obstet Gynecol 1992;167:1121–4.)