Labor is the physiologic process by which a fetus is expelled from the uterus to the outside world. Labor is defined as an increase in myometrial activity or, more precisely, a switch in the pattern of myometrial contractility from irregular contractures (long-lasting, low-frequency activity) to regular contractions (high-intensity, high-frequency activity),¹ resulting in effacement and dilatation of the uterine cervix. In normal labor, there appears to be a time-dependent relation between the biochemical changes in the connective tissue in the cervix that usually precede uterine contractions and cervical dilatation. All these events usually occur before the spontaneous rupture of the fetal . . .