Objectives: Vaginal birth after cesarean section (VBAC) is association with a small but significant risk of uterine rupture with poor outcomes for both mother and infant. Any attempt to induced labor increases the risk of uterine rupture in VBAC. Our objective is to determine whether cervical length predicts risk of postterm induction of VBAC.

Methods: This prospective study was conducted in 114 patients of VBAC out patient clinic. Cervical length was measured by a 7.5-MHz transvaginal transducer between 36+0 and 37+6 weeks of gestation. The primary outcome was the rate of deliveries after 41 weeks. We constructed a receiver operator characteristic (ROC) curve to determine the optimal cut-off point of the cervical length, to predict postterm delivery.

Results: 32 (28%) patients was delivered after 41 weeks. The ROC curve showed that the optimal cut-off point of cervical length was 2.4 cm. The predictive values of cervical volume on delivery after 41 weeks were: 87.5% of sensitivity; 23.2% of specificity; 82.6% of negative predictive value; 30.8% of positive predictive value, respectively.

Conclusion: This paper is one of a series that will adress patient factors, hospital factors, and clinical policies associated with VBAC outcome. The cervical length assessment is good tool in predicting postterm delivery. Long cervical length could be considered clinical risk factor of VBAC. After futher study, that will be used informed consent, risk assessment and selection of candidates.