Biodynamics of the cervical dilatation in human labor.

We recorded the pressure between the fetus and birth canal (PFB) with small strain-gauge type pressure transducers in 37 cases of human labor and estimated expulsive activity for evaluation of the expulsive forces. Expulsive activity increased progressively in conjunction with cervical dilatation and markedly increased after rupture of the membranes. At less than 200 Hashimoto units of expulsive activity, the cervical canal could not be dilated and labor was prolonged in all periods of the first stage of labor. There were three types of modes of changes in the expulsive activities at three points on the cervical canal. These three types had different clinical characteristics of cervical dilatation during labor. New parameters such as the expulsive effort, efficiency index and resistance index of the uterine cervix, estimated together with the expulsive activity, were proposed in an attempt to evaluate the effect of expulsive forces on cervical dilatation.