The use of sonographic myometrial thickness measurements for the prediction of time from induction of labor to delivery.

Background: Several attempts have been made to find tools for the prediction of successful induction of labor. Sonographic myometrial thickness has not yet been investigated regarding its use as a clinical tool for the course of labor induction.

Objective: To evaluate the role of sonographic measurement of myometrial thickness in the prediction of the time interval to successful vaginal delivery after induction of labor.

Study Design: A prospective study was conducted including term singleton pregnancies with a vertex presentation designated for balloon induction at 38-42 weeks gestation. Prior to induction, abdominal sonographic myometrial thickness was assessed at five locations: lower uterine segment (above and below the reflection of the urinary bladder), mid-anterior wall, fundus and posterior uterine wall. Induction of labor was then carried out with a trans-cervical Foley catheter that was substituted with intravenous oxytocin after balloon expulsion. The parameters assessed were successful induction of labor resulting in a vaginal delivery and the time interval from balloon insertion to balloon expulsion, the time interval from initiation of oxytocin administration to delivery and the total time from balloon insertion to delivery.

Results: Fifty-two women were recruited to the study. Indications for labor induction were: post-date pregnancy (48.1%), gestational diabetes mellitus (19.2%), oligohydramnios (11.5%), gestational hypertensive disorders (5.8%) and other indications (15.4%). Vaginal delivery was achieved in 46 patients (88.5%). A statistically significant correlation was found between fundal and posterior uterine wall myometrial thickness and time from induction to balloon expulsion (r = 0.36, p = 0.03; r = - 0.35, p = 0.05, respectively). This correlation remained significant in a multivariate logistic regression model controlling for confounders. A correlation between myometrial thickness and the total time from induction to delivery was not statistically significant.

Conclusion: Myometrial fundal and posterior uterine wall thickness in women undergoing labor induction with a balloon catheter was found to be correlated with the interval from balloon insertion to expulsion. Our findings support further investigations into the use of sonographic myometrial thickness as part of the assessment prior to induction of labor.