The effect of oxytocin infusion on uterine activity levels in slow labour.

Uterine activity was studied in 31 women who were progressing slowly in spontaneous labour. In 75%, levels of uterine activity were below the tenth centile for normal spontaneous labour (mean uterine activity integral, UAI, 593 kPas/15 min; SD 296). Following oxytocin infusion, there was a significant increase in uterine activity to a mean of 1124 kPas/15 min (SD 276), which was the same as in normal spontaneous labour. The response to oxytocin was dependent upon the pre-existing level of uterine activity, and sensitivity to oxytocin, rather than the dose rate; 84% responded to infusion rates of less than 8 mU/min. The response to oxytocin was best expressed in terms of active contraction area (uterine activity integral, UAI) or Montevideo units, rather than the frequency or active pressure of contractions. The rate of cervical dilatation following oxytocin augmentation could not be predicted either by the increase in uterine activity or by the actual level of activity achieved.