Head-to-cervix forces and their relationship to the outcome of labor

The force (as distinct from pressure) between the fetal head and the maternal cervix during labor was measured for the first time in an attempt to improve the intrapartum prediction of progress in labor. The 50th percentile of the variables active pressure and active force and the mean uterine activity integral were compared with the cervical dilatation rate and delivery mode in 31 women. The 50th percentile of active force had the highest correlation with the cervical dilatation rate (r = 0.54) (50th percentile of active pressure, r = 0.43; mean uterine activity integral, r = 0.40). The 50th percentile of active force was significantly higher in women who achieved a vaginal delivery (mean +/- SD 45 +/- 21.2 g wt) than in those who underwent cesarean delivery for failure to progress (16.5 +/- 9 g wt). The 50th percentile of active force discriminated among modes of delivery as effectively as did the cervical dilatation rate. These results support the hypothesis that head-to-cervix force measurements may have clinical value in the management of labor.