Novel approach to oxytocin induction-augmentation of labor. Application of oxytocin physiology during pregnancy.

New information and understanding about the physiology of oxytocin (OT) have provided the bases of novel and rational approaches to the induction and augmentation of labor with OT. Based on a half-life of 8-10 min and time to steady state of 20 min, the interval between intravenous OT dose increments during uterine stimulation should be 20-30 min. Feto-maternal blood plasma gradients of OT concentration in spontaneous labor at term indicate a feto-uterine flow of 2-4mU OT/min. Labor can be successfully induced in most women with such physiological doses (2-6 mU/min) of OT given intravenously. Direct and indirect evidence show that OT is released in pulses with the frequency and/or amplitude of the pulses increasing with or during spontaneous labor. Further OT interaction with its receptor renders it occupied and temporarily unavailable. We have therefore employed these observations to induce and augment labor with pulsatile intravenous administration of OT. In a prospective randomized study of 106 patients undergoing labor induction with pulsatile versus continuous administration of OT, the total dose, the average dose/min, and the peak or highest dose required/min were significantly reduced with pulsatile OT compared with continuous OT. These significant differences remained when controlled for parity, Bishop's score of cervical ripeness, and the number of days for induction. Similarly in a prospective randomized study on augmentation of labor by intravenous OT, we found the dose of OT for successful augmentation was significantly reduced with pulsatile OT compared with continuous OT. Thus, pulsatile OT not only is safe and requires less OT for uterine stimulation, but also constitutes a more physiological basis for uterine stimulation.