Preinduction Sonographic Measurement of Cervical Length
and Bishop Score in Predicting Successful Labor Induction

Rüya DEVEER, Mustafa UĞUR, Selen TAFLAN, Nurcihan K. HASÇELİK, Dilek UYGUR Tamer MUNGAN
Ankara-Turkey

OBJECTIVE: to investigate whether transvaginal ultrasonographic cervical measurement or Bishop score could predict better successful induction of labor
STUDY DESIGN: This prospective study recruited women with singleton gestations (42.4% were nulliparaus, 57.7% were multiparous) scheduled for induction of labor at >37 week.Transvaginal ultrasound and digital vaginal examinations were performed on 92 women, immediately before labor induction. Each by operators masked to the other measurement. İnduction of labor was performed according to our labor induction protocol as intravenous oxytocin.Data were collected on parity, gestational age, mode of delivery, BMI, induction-to-delivery interval,Bishop score and cervical length measurement.
RESULTS: Vaginal delivery occured in 77.2% of the patients (71); the remaining 22.8% underwent cesarien delivery (21). In 75 (77.3%) of these, delivery was within 12 h of induction. With mode of delivery used as primary outcome, women with a cervical length <26 mm were more likely to be delivered vaginally (p<0.001) as were women with a Bishop score >5 (p<0.001) A receiver operating characteristic curve (ROC) constructed to determine the best threshold value of Bishop score and cervical length to predict the vaginal delivery within 12 hours. These two curves were similarly shallow.The curve for the Bishop score showed an optimized cut off value of 5,corresponding to a sensitivity of 71.9%,specificity of 77.1%. The curve for sonographic measurement of cervical lenght showed an optimized cut off value of 26 mm corresponding to a sensitivity of 73.9% and specificity of 80% Both Bishop score and cervical lenght showed a linear correlation with duration of labor (r= -0.70, r= 0.65 respectively). When a logistic regression model was constructed, only Bishop score and BMI were independent predictors of mode of delivery (p=0.045, p=0.028 respectively)
CONCLUSION: Our study has demonsrated that induction to delivery interval significantly associated with both preinduction Bishop score and sonographically measured cervical lenght. Both sonographic cervical assessment and the Bishop score successfully predicted vaginal delivery within 12 h. Bishop score and cervical length may contribute in the prediction of the mode of delivery and induction to delivery interval.Among women with unfavourable cervix (bishop score of <5), transvaginal ultrasonographic measurement of cervical length may be an effective method in management of travay and obstetric prognoses, if the reasons for the induction are as postdate pregnancy, preeclampsi, etc.
(Gynecol Obstet Reprod Med 2005; 11:171-175)

Key Words: Cervical length, Bishop score, Labor induction