P39.16: Sonographic measurement of the lower uterine segment thickness: Need for a consensus to predict uterine rupture

Uterine rupture during trial of vaginal birth after caesarean (VBAC) remains a rare but dramatic obstetrical emergency. Although several studies have shown that sonographic evaluation of the lower uterine segment (LUS) near term can predict uterine rupture, the best measuring technique and the cut-off values to be used remain controversial. While a large prospective study demonstrated that an abdominal measurement of the full LUS thickness over 3.5 mm had a strong negative predictive value, other authors suggested to measure the muscular layer only with a cut-off value of 1.5 to 2.0 mm. We report a case of uterine rupture in a healthy 31-year-old patient, which had a prior low transverse caesarean seven years earlier with a single layer closure of hysterotomy. At 36 weeks of gestation, the transvaginal sonographic measurement of the LUS was respectively 3.6 mm for the full thickness and 1.1 mm for the muscular layer only. At 39 weeks', induction of labor for premature rupture of membranes was initiated with oxytocin. A fetal bradycardia occurred approximately 12 hours after the initiation of induction. The patient underwent an emergency caesarean for clinical evidence of uterine rupture. Operative findings revealed a large uterine lateral tear from the cervix to the uterine cornu with the infant lying in the upper abdomen. In this case, there was a discrepancy between the normal full LUS thickness and the thin muscular layer. As the myometrium measurement could be more representative of the LUS resistance, we should perhaps give more credit to result of the later before proposing a trial of VBAC. Evidently, other risk factors must be taken into account, such as the type of closure of the uterine segment at prior caesarean and the intrapartum assessment. This case emphasizes the need for a consensus on the measuring techniques and cut-off values of the LUS thickness and to investigate its role in estimating the risk of uterine rupture among other predicting factors.