An experimental approach to a simplified model of human birth

This study presents a simplified experimental model of labor for the study of fetal lie and amniotic fluid properties. It mimics a ventouse (vacuum extraction) delivery to study the effect of amniotic fluid properties on force transfer to a passive fetus. The simplified vacuum delivery consists of a solid ovate spheroid being pulled from a passive, flexible spherical elastic shell filled with fluid. We compare the force necessary to remove the ovate fetus in fluids of varying properties. Additionally, the fetal lie-angular deviation from maternal/fetal spinal alignment-is changed by 5° intervals and the pullout force is measured. In both the concentric ovate experiments, the force to remove the fetus changes with the properties of the fluid occupying the space between the fetus and the uterus. Increasing the fluid viscosity by 35% decreases the maximum fetal removal force by up to 52.5%. Furthermore, while the force is dominated by the elastic force of the latex uterus, the properties of the amniotic fluid can significantly decrease the total removal force. This study demonstrates that the fluid components of a birth model can significantly alter the forces associated with fetus removal. This suggests that complete studies of human parturition should be designed to include both the material and fluid systems.