Determination of myometrial tension during labor by combined microtransducer IUP-rcording and ultrasonic examination of the uterine cavity.

In twelve women, in whom labor was induced by oxytocin infusion, intra-uterine pressure (IUP) was recorded by micro-transducers, and simultaneously the diameter of the uterine cavity was estimated by means of ultrasound. Myometrial tension was calculated according to the law of Laplace. In the ten women who were delivered within eight hours after the start of induction, myometrial tension was clearly higher than in the two in whom induction failed. No technical problems were encountered during the registrations, which in some cases lasted for more than five hours. It is suggested that with the described technique, a more accurate determination of myometrial activity is possible than with the generally used methods for IUP recording. The technique might facilitate evaluation of drug effects on the uterus during labor, and improve the IUP-part of intrapartum clinical monitors.