Bishop score and the outcome of labor induction with misoprostol.

Background: The aim of the study was to retrospectively identify possible factors for predicting the outcome of induction with misoprostol.

Methods: Fifty micrograms of misoprostol were administered intravaginally every 6 h during the first 2 days of induction, up to a maximum of 4 doses. The Bishop score, indication for induction, gestational length, maternal age, and parity were analyzed. The study involved 99 patients (47 primiparous and 52 multiparous) at term (>36 weeks of gestation) with unripe cervices.

Results: Forty-five per cent of the patients achieved ripening of cervix and went into labor after a single dose of misoprostol; a further 45% required 2 doses. Nine patients received more than 2 tablets. Ninety-seven per cent of all vaginal deliveries occurred within the first 2 days of induction. Ninety-five per cent of the patients delivered vaginally when the Bishop score was >3, compared with 75% of those with a Bishop score of < or =3 (p=0.003). Among factors creating the Bishop scoring system, in logistic regression analysis effacement of the cervix was the only independent, significant predictor of cesarean section (p=0.003, OR = 0.16) even after adjusting for maternal age, which also was a significant predictor in the regression analysis. Eleven patients had previously had a cesarean section; one of them had a uterine rupture with a fatal outcome for the fetus. All women with a previously scarred uterus are now excluded from misoprostol treatment.

Conclusion: Misoprostol 50 microg administered intravaginally every 6 h according to this protocol is highly effective for inducing labor in carefully selected patients with unripe cervices.