Bishop score and transvaginal ultrasound for preinduction cervical assessment: a randomized clinical trial.

OBJECTIVE

To compare transvaginal ultrasound with the Bishop score in assessment of cervical ripening for choice of induction agent.

METHODS

Eighty women were randomized to have preinduction cervical assessment for choice of induction agent based on either Bishop score or transvaginal ultrasound. The primary outcome measure was the percentage of women who were administered prostaglandin as a preinduction agent. The criteria for considering the cervix as unripe and thus for using prostaglandin were either a Bishop score < 6 or a cervical length > 30 mm with cervical wedging of < 30% of the total cervical length. Secondary outcome measures included interval to active phase, interval to delivery and rate of Cesarean section.

RESULTS

While 85% of women received prostaglandin in the Bishop score group, only 50% of them did in the transvaginal ultrasound group (P = 0.001). The interval to active phase, interval to delivery and rate of Cesarean section were similar in both groups.

CONCLUSIONS

With the suggested cut-off values of a Bishop score < 6 or a cervical length > 30 mm and wedging < 30%, the use of transvaginal ultrasound instead of Bishop score for preinduction cervical assessment to choose induction agent significantly reduces the need for intracervical prostaglandin treatment without adversely affecting the success of induction.