Units for the evaluation of uterine contractility

An improved system of units is proposed for evaluating the contractile activity of the myometrium. Mean active pressure (in kPa) provides the best overall measure of contractility. This measure is broadly compatible with studies quoting 'uterine activity integral' in kPa s per 15 min, but may be applied to any period of time. Units are suggested for measuring the amplitude, frequency and duration of contractions. It is shown that these are independent variables, and that mean active pressure is the numerical product of these three components.