A prospective study on comparison of cervical length measured transvaginally and bishop score in predicting successful labour induction

T. E. Balaji, Vijaya S.


Background: Induction of labour is one of the common interventions in obstetric practice. Cervical assessment has been used as a prediction of the successful vaginal delivery. This study is designed to investigate transvaginal ultrasonographic cervical measurement as a predictor of duration of labour and successful induction resulting in vaginal delivery and compare the performance of ultrasonographic cervical measurement with that of the Bishop score in predicting the outcome of labour induction.

Methods: It is a prospective observational study. In this study, for the 100 primigravida women with gestational age of 37-42 weeks of gestation admitted for induction of labour, the cervical length was measured by transvaginal ultrasound and then Bishop Score was assessed by digital examination. Predictive values for successful labour induction were detected and compared.

Results: Using Spearman’s rho correlation both TVS cervical length and Bishop score have significant correlation in predicting the success of induction of labour. Cervical length is the better predictor of the likelihood of delivering vaginally within 24hrs.  In the receiver operating characteristic curves, the best cut-off points for the prediction of successful induction was 26mm for cervical length and 4 for the Bishop Score. However, TVS cervical length appears to be a better predictor than the Bishop Score, with a sensitivity of 58.1% and a specificity of 100% compared to 70.3% and 45.5% respectively.

Conclusions: Transvaginal sonographic measurement of cervical length is a better predictor of the likelihood of successful induction of labour within 24hrs of induction and increased vaginal deliveries within 48 hours of induction when compared to Bishop Score.


Bishop score, Cervical length, Induction of labour, Transvaginal ultrasound

Full Text:



RCOG. Induction of labour. In Evidence based Clinical Guideline Number 9 London:2001.

Bishop EH. Pelvic scoring for elective induction. 1964;24:266-8.

Iams JD. The length of the cervix and the risk of spontaneous premature delivery. National Institute Of Child Health and Human development Maternal Fetal Medicine Units Network.1996;334:567-72.

Vonda Ware. Transvaginal Ultrasonographic cervical measurement as a predictor of successful labor induction.182(5)2000:1030-2.

Cunningham FG. Induction and augmentation of labor. 21st Ed. New York, Ny: MC Graw-Hill; 2001:469-81.

Bishop EH. Pelvic scoring for elective induction. 1964;24:266- 8.

Harrison RF, Flynn M, Craft I. Assessment of factors constituting an inducibility profile. 1977;49: 270.

Lange AP. Pre labor evaluation of pre induction scoring systems. 1982;60:137.

O Leary J, Ferrel RE. Comparison of Ultrasonographic and digital cervical evaluation. 1986;69:718-9.

Peterson Brown S, Fisk NM, Edmonds DK, Rodeck CH. Preinduction cervical assessment by Bishop score and transvaginal ultrasound. Eur J Obstst Gynecol Reprod Biol. 1991;40:17-23.

Boozarjomehri F, Timor-Tritsch I, Chao CR, Fox HE. Transvaginal ultrasonographic evaluation of the cervix before labor: presence of cervical wedging is associated with shorter duration of induced labor. Am J Obstet Gynecol. 1994;171:1081-7.

Watson WJ, Stevens D, Welter S, Day D. Factors predicting successful labor induction. Obstst Gynecol 1996;88:990-2.

Gonen R, Degani S, Ron A. prediction of successful induction of labor. Comparison of transvaginal ultrasonography and the Bishop Score. Eur J Ultrasound. 1998;7:183-7.

Ware V, Raynor D. Transvaginal ultrasonographic cervical measurement as a predictor of successful labor induction. Am J Obstet Gynecol. 2000;182:1030-2.

Pandis. Preinduction sonographic measurement of cervical length in the prediction of successful induction of labor. Ultrasound Obstet Gynecol. 2001;623-8.

Rozenberg P. Comparison of digital and ultrasonographic examination of the cervix in predicting time interval from induction to delivery in women with a low bishop score. BJOG. 2005;112:192-6.