Models for the prediction of successful induction of labor based on pre-induction sonographic measurement of cervical length.

OBJECTIVE: To examine the effect of pre-induction cervical length, parity, gestational age at induction, maternal age and body mass index (BMI) on the possibility of successful delivery in women undergoing induction of labor. METHODS: In 822 singleton pregnancies, induction of labor was carried out at 35 to 42(+6) weeks of gestation. The cervical length was measured by transvaginal sonography before induction. The effect of cervical length, parity, gestational age, maternal age and BMI on the interval between induction and vaginal delivery within 24 hours was investigated using Cox's proportional hazard model. The likelihood of vaginal delivery within 24 hours and risk for cesarean section overall and for failure to progress was investigated using logistic regression analysis. RESULTS: Successful vaginal delivery within 24 hours of induction occurred in 530 (64.5%) of the 822 women. Cesarean sections were performed in 161 (19.6%) cases, 70 for fetal distress and 91 for failure to progress. Cox's proportional hazard model indicated that significant prediction of the induction-to-delivery interval was provided by the pre-induction cervical length (HR=0.89, 95% CI 0.88-0.90, p<0.0001), parity (HR=2.39, 95% CI 1.98-2.88, p<0.0001), gestational age (HR=1.13, 95% CI 1.07-1.2, p=or<0.0001) and birth weight percentile (HR=0.995, 95% CI 0.99-0.995, p=0.001), but not by maternal age or BMI. Logistic regression analysis indicated that significant prediction of the likelihood of vaginal delivery within 24 hours was provided by pre-induction cervical length (OR=0.86, 95% CI 0.84-0.88, p<0.0001), parity (OR=3.59, 95% CI 2.47-5.22, p<0.0001) and gestational age (OR=1.19, 95% CI 1.07-1.32, p=or<0.0001) but not by BMI or maternal age. The risk of cesarean section overall was significantly associated with all the variables under consideration, i.e., pre-induction cervical length (OR=1.09, 95% CI 1.06-1.11, p<0.0001), parity (OR=0.25, 95% CI 0.17-0.38, p<0.0001), BMI (OR=1.85, 95% CI 1.24-2.74, p=0.0024), gestational age (OR=0.88, 95% CI 0.78-0.98, p=0.0215) and maternal age (OR=1.04, 95% CI 1.01-1.07, p=0.0192). The risk of cesarean section for failure to progress was also significantly associated with pre-induction cervical length (OR=1.11, 95% CI 1.07-1.14, p<0.0001), parity (OR=0.26, 95% CI 0.15-0.43, p<0.0001), gestational age (OR=0.83, 95% CI 0.73-0.96, p=0.0097) and BMI (OR=2.07, 95% CI 1.27-3.37, p=0.0036). CONCLUSION: In women undergoing induction of labor, pre-induction cervical length, parity, gestational age at induction, maternal age and BMI have a significant effect on the interval between induction and delivery within 24 hours, likelihood of vaginal delivery within 24 hours and the risk of cesarean section.

The value of ultrasound in the prediction of successful induction of labor.

OBJECTIVES: To examine the value of pre-induction sonographic assessment of cervical length, posterior cervical angle and occipital position in the prediction of the induction-to-delivery interval within 24 h, the likelihood of vaginal delivery within 24 h, the likelihood of Cesarean section and to compare sonographic assessment with the Bishop score. METHODS: In 604 singleton pregnancies, induction of labor was carried out at 35-42 weeks of gestation. Immediately before induction, transvaginal sonography was performed for measurement of cervical length and posterior cervical angle and a transabdominal scan was carried out to determine the position of the fetal occiput. The value of occipital position, posterior cervical angle, cervical length, parity, gestational age, maternal age, and body mass index (BMI) on the induction-to-delivery interval within 24 h, the likelihood of vaginal delivery within 24 h and the likelihood of Cesarean section were investigated by Cox proportional hazard model or logistic regression analysis. RESULTS: Vaginal delivery occurred in 484 (80.1%) women and this was within 24 h of induction in 388 (64.2%). Cesarean section was performed in 120 (19.9%). Occiput-anterior (OA) and transverse (OT) positions were analyzed as one group as the odds ratios (OR) and the HR were similar and different from occiput-posterior (OP), which was analyzed as another group. Prediction of the induction-to-delivery interval was provided by the occipital position, pre-induction cervical length, parity and posterior cervical angle. Prediction of the likelihood of vaginal delivery within 24 h was provided by the occipital position, cervical length, posterior cervical angle and BMI. Prediction of the likelihood of Cesarean section was provided by the occipital position, cervical length, parity, maternal age and BMI. In the prediction of vaginal delivery within 24 h, for a specificity of 75%, the sensitivity for ultrasound findings was 89% and for the Bishop score it was 65%. The respective sensitivities for Cesarean section were 78% and 53%. CONCLUSION: In women undergoing induction of labor, significant independent prediction of the induction-to-delivery interval within 24 h, the likelihood of vaginal delivery within 24 h and the likelihood of Cesarean section are provided by pre-induction cervical length, occipital position, posterior cervical angle and maternal characteristics. Sonographic parameters were superior to the Bishop score in the prediction of the outcome of induction.

Pre-induction sonographic measurement of cervical length in prolonged pregnancy: the effect of parity in the prediction of induction-to-delivery interval.

OBJECTIVE: To examine the effect of parity on the relationship between pre-induction cervical length and the induction-to-delivery interval and rate of vaginal delivery within 24 h in women undergoing induction of labor for prolonged pregnancy. METHODS: In 382 singleton pregnancies, induction of labor was carried out at 41 + 3 to 42 + 1 weeks of gestation. The cervical length was measured by transvaginal sonography before induction. Univariate analyses were performed by constructing Kaplan-Meier survival curves for the induction-to-delivery interval for various subgroups, and comparing these using log rank tests. Multivariate analyses were performed using the Cox proportional hazards model and multiple linear regression. RESULTS: Successful vaginal delivery within 24 h of induction occurred in 67% of the women and the pre-induction cervical length was significantly associated with the induction-to-delivery interval and the rate of vaginal delivery within 24 h. Sonographically measured cervical length was better than the Bishop score or cervical length by vaginal examination in predicting the outcome of induction. Parity provided a significant independent contribution, in addition to pre-induction cervical length, in the prediction of the outcome of labor. Thus, in multiparae the incidence of successful vaginal delivery within 24 h of induction was about 30% higher than in nulliparae. For the same cervical length, the induction-to-delivery interval in multiparae was 37% lower than in nulliparae. CONCLUSION: In women undergoing induction of labor for prolonged pregnancy, cervical length and parity provide independent prediction of induction-to-delivery interval and the likelihood of vaginal delivery within 24 h of induction.

Pre-induction sonographic measurement of cervical length in prolonged pregnancy: the effect of parity in the prediction of the need for Cesarean section.

OBJECTIVE: To examine the effect of parity on the relationship between pre-induction cervical length and the risk of Cesarean section in women undergoing induction of labor for prolonged pregnancy. METHODS: In 382 singleton pregnancies, induction of labor was carried out at 41 + 3 to 42 + 1 weeks of gestation. The cervical length was measured by transvaginal sonography before induction. In 71 of these cases a Cesarean section was required for either fetal distress or failure to progress and 311 women delivered vaginally. The effect of parity and pre-induction cervical length on the risk of Cesarean section was examined. RESULTS: In nulliparous women the incidence of Cesarean section was significantly higher than in multiparous women (28.1% vs. 8.9%). In both nulliparae and multiparae there was a significant association between pre-induction cervical length and the rate of Cesarean section. Logistic regression analysis demonstrated that cervical length and parity provided significant independent prediction of all Cesarean sections and Cesarean sections for failure to progress. The odds of Cesarean section increased by about 10% with each increase of 1 mm in cervical length, over the mean cervical length of 20 mm for nulliparae and 18 mm for multiparae, and the odds was about 75% lower in multiparae, compared to nulliparae with the same cervical length. Receiver-operating characteristics curves (ROC) demonstrated that cervical length was better than the Bishop score in the prediction of all Cesarean sections (area under ROC = 0.72 vs. 0.68) and Cesarean sections for failure to progress (area under ROC = 0.76 vs. 0.69). CONCLUSION: In women undergoing induction of labor for prolonged pregnancy, cervical length and parity provide significant independent prediction of the likelihood of Cesarean section.