Comparative study between transvaginal ultrasonographic cervical measurement and Bishop Score as predictors of successful induction of labor

Summary and conclusionAssessment of the cervix is important in evaluating the women undergoing induction of labor. Digital examination gives valuable informations but it is subjective and may cause infection in cases with premature rupture of the membrane (PROM). Sonographic assessment of the cervix is more objective than digital assessment and helps to guide clinical management.Transvaginal sonography of the cervix overcomes the limitations of transabdominal sonography and is more precise and objective in evaluating pregnant women prior to labor induction.A ploicy of labor induction at 41 weeks of gestation for uncomlpicated sigelton pregnancies reduces cesarean delivery rates without compromising perinatal outcomes (ACOG, 2003). Risk to both mother and infant increase as pregnancy progresses beyond 40 weeks of gestation (ACOG, 2004).This study was carried out in Department of Obstetrics and Gynecology, Zagazig University Hospitals. 50 cases with prolonged pregnancy underwent induction of labor. For every woman undertaken in the study, the following was done: Full history taking, clinical assessment, TVS to evaluate cervical length, vaginal examination to detect Bishop Score. Induction was done by 50 mcg misoprostol intravaginally every 6 hours with a maximum of 4 doses.The cases were divided according to the outcome of induction into 3 groups:Group I: Induction was successful, 38 cases were delivered vaginally within 24 hours (76%).Group II: Induction was of delayed success; one case was delivered vaginally but after 24 hours (2%).Group III: Induction was failed, 11 cases were delivered by cesarean section (22%), 8 of them due to cervical dystocia and 3 cases due to fetal distress.The 3 group were  41 weeks and the parity ranging from 0 to 4. The Bishop Score ranged between 3 and 9 with mean of 5.24  1.3.The cervical length measured by transvaginal ultrasonography ranged from 13.7 mm and 40.0 mm with mean length 30.9  5.9 mm.The mean duration of labor induction was 11.9  5.7 hours with a range of 6 to 30 hours.The duration of the latent phase of labor was of no statistical significance in relation to the Bishop Score and sonographically measured cervical lengthBoth the Bishop Score and the cervical length measured by TVS showed a linear correlation with the duration of labor induction (R = 0.86, P<0.001 for cervical length) and (R = -0.77, P <0.001 for Bishop Score) also the Bishop Score and cervical length by TVS correlated with each other (R = -0.9 and P <0.001). Women with a Bishop Score > 5 had significantly shorter labors than those with Score  5 (mean 10.9  3.5 vs. 20.15  4.8 hours, P >0.01 significant). Similarly with a cervical length <30 mm were delivered in shorter time than those with cervical length  30 cm (9.7  2.67 vs. 16.9  5.6 hours, P >0.01 significant).It was found that vaginal delivery is closely associated with Bishop Score more than 5 and sonographically measured cervical length less than 30 mm. The cervical length at cut-off point 30 mm was significantly associated with the success of labor induction however the Bishop Score at cut-off point 5 was statistically non significant in relation to the success of labor induction.When a receiver operating characteristic curve was used the 30 mm cut off point for cervical length was the best predictor of vaginal delivery with a sensitivity of 90.9% and a specificity of 51.3% and accuracy of 60%.ConclusionSuccess of labor induction in women undergoing induction due to prolonged pregnancy can be highly predicted by transvaginal sonography of cervical length as it is more objective and accurate than Bishop Score. The 30 mm cut-off point for cervical length was the best predictor of vaginal delivery with a sensitivity of 90.9% and a specificity of 51.3% and accuracy of 60%