not all of these inductions result in vaginal delivery , and some result in emergency cesarean sections . compared with spontaneous onset of labor , induction of labor is complicated by a higher rate of cesarean section , occurring in one - fifth of women who undergo induction.1,2 an issue of interest for reproductive health researchers is finding better methods for predicting an unwanted type of delivery after induction of labor . the bishop score is an index known to predict outcome of labor , but it does not provide satisfactory results , due to a low predictive value , especially in predicting cesarean section . it is not too sophisticated a procedure to be done in obstetric units and clinics . attempts have been made in the past to use transvaginal ultrasonography for prediction of type of delivery , and efforts have been made to explore if its predictive value is higher than that of the bishop score or not . however , controversial results have been published , and not enough evidence is available to consider it as a strong alternative to the bishop score . the aim of this study was to compare the predictive value of transvaginal ultrasonographic findings and the bishop score for cesarean section as an outcome of induction of labor . two hundred pregnant women admitted for induction of delivery were enrolled in this prospective study . they were hospitalized at alzahra university hospital in tabriz , northwest iran , in 20072009 . women with pregnancies at 3742 weeks gestational age who agreed to participate were considered eligible for the study . the study protocol was approved by the ethics committee at tabriz university of medical sciences . inclusion criteria were a singleton pregnancy , cephalic presentation , gestational age more than 37 weeks , and a live pregnancy . to prevent iatrogenic premature rupture of membranes , those with cervical dilatation cervical length and posterior cervical angle were measured by transvaginal sonography , using an aloka-350 ultrasound machine and a 15 mhz convex probe . posterior cervical angle , defined as the angle between the cervical canal and the posterior uterine wall , was measured using the trace function of the ultrasound machine.3 bishop score was assessed by digital examination prior to induction . data were entered into the computer and analyzed using the stata 11 statistical software package ( stata corporation , college station , tx ) . descriptive sensitivity and specificity statistics were calculated . to compare the predictive value of the methods , receiver - operating characteristic ( roc ) curves were plotted and equality of the area under the curve ( auc ) was tested . data were entered into the computer and analyzed using the stata 11 statistical software package ( stata corporation , college station , tx ) . the predictive value of the methods , receiver - operating characteristic ( roc ) curves were plotted and equality of the area under the curve ( auc ) was tested . mean age (  standard deviation [ sd ] ) of the participants was 29.9 ( 5.6 ) years , mean gestational age was 39.6 ( 1.4 ) years , and mean gravid was 1.5 ( 0.8 ) . up to 10% of the participants declared a previous abortion history , up to 10% were illiterate , and two - thirds were nulliparous . of 200 deliveries , 143 ( 71.5% ) were vaginal and 57 ( 28.5% ) were by cesarean section . the first - minute apgar score in half of the neonates was 9 , 6 in one , and 8 in 18 cases . except for two babies with a 5-minute apgar score = 8 , the babies had higher scores at the fifth minute . table 1 presents sensitivity , specificity , and correct classification rates for the different methods of predicting cesarean section . the wide range of cut points was truncated to those producing more acceptable sensitivity and specificity . the roc curves for bishop score , cervical length , and posterior cervical angle for predicting cesarean section versus vaginal delivery are compared in figures 1 and 2 . the auc for cervical length measured by ultrasonography was 0.69 ( 95% ci 0.60.77 ) . the auc for posterior cervical angle measured by ultrasonography was 0.38 ( 95% ci 0.290.47 ) . the roc for cervical length was significantly different from both bishop score and posterior cervical angle ( p < 0.001 ) . however , the difference for auc compared for bishop score and posterior cervical angle was not statistically significant . bishop score was correlated with posterior cervical angle ( r = 0.24 , p < 0.001 ) . it was inversely correlated with cervical length ( r = 0.51 , p < 0.001 ) and interval until induction of delivery ( r = 0.21 , p < 0.01 ) . induction interval was not found to be correlated with posterior cervical angle , but was correlated with cervical length ( r = 0.22 , p < 0.01 ) . imaging versus clinical assessment has always been a challenge for choosing diagnostic or prognostic measures , sometimes showing simple clinical prediction scores to be as good as sophisticated imaging facilities.3,4 in the present study , cervical length measured by transvaginal ultrasonography was found to be a better predictor of an unsuccessful labor leading to cesarean section than the bishop score . however , the ability of the posterior cervical angle to predict cesarean section was not much different from that of the bishop score . several previous studies have compared ultrasonographic findings with the bishop score in assessing the success of induction . most of these studies have used smaller sample sizes than ours , and few have had larger samples . regardless of slight differences in methodology , all the larger - scale studies , like ours , have found cervical length to be a better predictor than bishop score.1,2,513 few have found cervical length to be the best predictor , few have prioritized the bishop score,1416 and two studies have not observed a difference in their predictive value.17,18 studies suggesting bishop score as the best predictor have not compared the auc or provided sensitivity and specificity measures for given cut points . none of the other studies mentioned have reported auc for cervical length to be < 0.66 and > 0.89 , and the aucs reported for bishop score vary widely , sometimes being as low as 0.46 . novakov - mikic et al reported findings somewhat similar to ours.13 however , they investigated the anterior cervical angle , the predictive value of which was even lower than ours . eggebo et al found the posterior cervical angle to be a predictor of success of induction , but in a regression model rather than an assessment of predictive value.19 based on our findings and the information available in the literature , it seems that cervical length measured by transvaginal ultrasonography has the potential to replace the traditional bishop score when such a facility can be made easily available . however , prior to general recommendation of this approach , cost - effectiveness studies will be necessary .