Factors predicting labor induction success: a critical analysis

Because of the risk of failed induction of labor, a variety of maternal and fetal factors as well as screening tests have been suggested to predict labor induction success. Certain characteristics of the woman (including parity, age, weight, height and body mass index), and of the fetus (including birth weight and gestational age) are associated with the success of labor induction; with parous, young women who are taller and lower weight having a higher rate of induction success. Fetuses with a lower birth weight or increased gestational age are also associated with increased induction success. The condition of the cervix at the start of induction is an important predictor, with the modified Bishop score being a widely used scoring system. The most important element of the Bishop score is dilatation. Other predictors, including transvaginal ultrasound (TVUS) and biochemical markers [including fetal fibronectin (fFN)] have been suggested. Meta-analyses of studies identified from MEDLINE, PubMed, and EMBASE and published from 1990 to October 2005 were performed evaluating the use of TVUS and fFN in predicting labor induction success in women at term with singleton gestations. Both TVUS and Bishop score predicted successful induction [likelihood ratio (LR)=1.82, 95% confidence interval (CI)=1.51-2.20 and LR=2.10, 95%CI=1.67-2.64, respectively]. As well, fFN and Bishop score predicted successful induction (LR=1.49, 95%CI=1.20-1.85, and LR=2.62, 95%CI=1.88-3.64, respectively). Although TVUS and fFN predicted successful labor induction, neither has been shown to be superior to Bishop score. Further research is needed to evaluate these potential predictors and insulin-like growth factor binding protein-1 (IGFBP-1), another potential biochemical marker.     

Preinduction cervical assessment

The rate of labor induction is increasing in the United States. Methods for quantifying cervical factors have been developed to identify patients who may benefit from cervical ripening before induction. The first cervical scoring systems used digital examination. More recently, cervical ultrasound and testing for the presence of fetal fibronectin have been suggested to evaluate cervical readiness for labor induction, but neither of these methods provides a significant improvement over digital examination. The Bishop score, the most widely used digital examination scoring system, still is the most cost effective and accurate method of evaluating the cervix before labor induction.     

应用胎儿纤连蛋白选择足月妊娠引产时机

目的探讨宫颈阴道分泌物胎儿纤连蛋白(fFN)定性测定能否指导足月妊娠引产时机的选择.方法64例初产、足月、头位、单胎、未破膜、未临产、3日内无同房史、无严重妊娠合并症、并发症,在引产开始前行宫颈阴道分泌物fFN定性测定,然后肛诊作宫颈Bishop评分,选用缩宫素引产.另有11例符合上述条件的孕妇,在引产过程中作fFN测定.结果fFN预示引产成功的敏感度61.7%,特异度70.59%,阳性预示率85.29%,阴性预示率40.00%,均优于宫颈Bishop评分.fFN(+)组引产成功的时间短于阴性组,引产次数也较阴性组少.当fFN(+)、宫颈触诊软时,90.9%在3天内引产成功;fFN(+)宫颈不软或fFN(-)、宫颈软时,引产成功率降为80%左右;fFN(-)、宫颈不软时,引产的成功率仅为44%.在引产过程中测定fFN,其结果与引产效果基本相符(8/11).结论fFN是反映宫颈成熟度的良好标志,较宫颈Bishop评分更正确、客观.定性测定宫颈阴道分泌物fFN可用于指导足月妊娠引产时机的选择,将fFN与Bishop评分,尤其宫颈的软硬度结合考虑将提高正确性.     

Lamicel for induction of labor

Lamicel is a synthetic osmotic cervical dilator currently used as a method of cervical dilation in first- and second-trimester pregnancy termination. It works by extracting fluid from the cervical tissue and softening the cervix. This study evaluated its effectiveness in nonelective medical induction of labor in high-risk patients. Forty inpatients who, for medical and obstetric reasons, required delivery within the next 24-48 hours were studied. Patients were evaluated to make certain that a 12- to 24-hour delay was safe for mother and child. The evening prior to the day of induction, a pelvic examination determined the Bishop score, and bacterial cultures were obtained from the endocervix. As many Lamicels as possible (usually one to three) were then placed in the endocervix without rupturing the membranes. The next morning the devices were removed, a repeat Bishop score obtained, amniotomy performed, internal monitors placed and oxytocin infusion initiated. Data were collected for preinsertion and postinsertion Bishop scores, induction-delivery times, duration of ruptured membranes, and cesarean and vaginal birth rates. Maternal and neonatal infectious morbidity was determined. A comparison group of patients with premature rupture of the membranes was selected. From data studied at our institution, patients were matched for parity and duration of labor (not significantly different from the Lamicel group). The study revealed that Lamicel can be an effective means of ripening the cervix for induction of labor.     

Variables that predict the success of labor induction

BACKGROUND. To analyze the clinical and sonographic variables that affect the success of labor induction. METHODS. Bishop score, cervical length, and parity were studied in 196 pregnant women in the prediction of successful vaginal delivery within 24 hr of induction. Logistic regression and segmentation analysis were performed. RESULTS. Cervical length [odds ratio (OR) 1.089, P<0.001], Bishop score (OR 0.751, P=0.001), and parity (OR 6.85, P<0.001) predict the success of labor induction. The best cut-off points for cervical length were <16.5, 16.5--27, and >27 mm (P=0.0016). In the analysis of the Bishop score, we also obtained three discriminatory points, 0, 1--4, and >4 (P=0.0006), that best predict the labor induction. Finally, in a global analysis of the variables studied, the best statistic sequence that predicts the labor induction was found when we introduced parity in the first place. The success of labor induction in nulliparous was 50.77 and 83.33% in multiparous (P=0.0001). CONCLUSIONS. Cervical length, Bishop score, and parity predict the success of labor induction.     

Cervical ripening.

Induction of labor is indicated when the benefits to either the mother or the fetus outweigh the benefits of continuing the pregnancy. The state of the cervix is clearly related to the success of labor induction and the duration of labor. In cases of unfavorable cervices, physicians usually use a ripening agent before inducing labor. Unfortunately, as reviewed in this article, the ideal ripening agent is not found yet. No method of cervical ripening has shown a consistent and significant reduction in CS rate. In fact, women with the most unfavorable cervices (Bishop score, < or = 2) still face high rates of induction failure and CS.     

Transvaginal ultrasonographic cervical measurement as a predictor of successful labor induction

OBJECTIVE: Our purpose was to compare transvaginal cervical measurement and the Bishop score as indicators of duration of labor and successful induction of labor at term.Study Design: This prospective observational study recruited women with singleton gestations scheduled for induction of labor at > or =37 weeks. Transvaginal ultrasonographic measurement of cervical length was performed and the Bishop score was determined, each by operators masked to the other measurement. Data were collected on parity, gestational age, mode of delivery, induction agent, induction-to-delivery interval, Bishop score, and cervical length measurement. RESULTS: A total of 77 women were analyzed. Vaginal delivery occurred in 69%. Both Bishop score and cervical length showed linear correlation with duration of labor (R(2) = 0.43, P <. 001; R(2) = 0.48, P <.001; respectively). Women with cervical length <3.0 cm had shorter labors (P <.001) and were more likely to be delivered vaginally (P <.001). Women with a Bishop score >4 also had shorter labors and were more likely to be delivered vaginally, with similar P values. A logistic regression model identified cervical length and parity as the only independent predictors of vaginal delivery. CONCLUSIONS: Both ultrasonographically measured cervical length and Bishop score predict duration of labor and likelihood of vaginal delivery. However, only cervical length and parity were independent predictors of mode of delivery.     

Effect of vaginal pH on efficacy of the dinoprostone gel for cervical ripening/labor induction

OBJECTIVE: The purpose of this study was to evaluate whether vaginal pH has an effect on the efficacy of the dinoprostone gel for cervical ripening/labor induction. STUDY DESIGN: Thirty-two women with an unfavorable cervix who were undergoing labor induction were enrolled in this prospective, double-blinded investigation. Initial vaginal pH and Bishop score assessment were made by an independent examiner. All women received cervical ripening with the dinoprostone gel 5 mg intracervically, with repeated dosing one time 6 hours later. Twelve hours later, oxytocin induction was initiated per standardized protocol, and outcome data were collected. RESULTS: Mean (+/-SD) initial vaginal pH was 4.7 +/- 0.6 (range, 4.0-6.0) for the study cohort. No significant differences were noted between women with a high vaginal pH (>4.5, n = 16 women) and women with a low vaginal pH (< or =4.5, n = 16 women) with respect to maternal age, parity, gestational age, or initial Bishop score. Although Bishop score change over the initial 12 hours of cervical ripening did not significantly differ between the high vaginal pH (2.3 +/- 2.3) and the low vaginal pH group (2.3 +/- 2.5, P = not significant), time to active labor (19 +/- 10 hours vs 33 +/- 17 hours, P =.001), complete dilation (24 +/- 10 hours vs 37 +/- 19 hours, P =.03), and delivery (26 +/- 10 hours vs 38 +/- 18 hours, P =.02) were significantly shorter in women with a high vaginal pH compared with women with a low vaginal pH, respectively. A significant association was noted between vaginal pH and time to active labor (r = -0.52, P =.003), complete dilation (r = -0.50, P =.006), and delivery (r = -0.44, P =.01); however, pH was not significantly associated with Bishop score change during the initial 12 hours of cervical ripening. CONCLUSION: Vaginal pH is an important factor that affects the efficacy of the dinoprostone gel as an adjuvant for labor induction.     

Comparison of ultrasonographic cervical length and the Bishop score in predicting successful labor induction

BACKGROUND: The aim of this study was to compare the performance of the Bishop score and transvaginal ultrasonography to predict successful labor induction, and to estimate the most useful cut-off points for the two methods. METHODS: The five components of the Bishop score were assessed by digital examination and cervical length was measured by transvaginal ultrasonography in 177 women with a single pregnancy, 36-42 weeks of gestation, and a live fetus in cephalic presentation before induction of labor. RESULTS: Multiple regression analysis showed that the Bishop score, cervical length, and parity provided independent contribution in the prediction of the likelihood of delivering vaginally within 60 h. The only component of the Bishop score that was independently predictive of the probability of vaginal delivery within 60 h was station. The best cut-off points for predicting successful induction using receiver operating characteristic curves were 24 mm for cervical length and 4 for the Bishop score. Cervical length was a better predictor than the Bishop score (sensitivity and specificity of 66 and 77% versus 77 and 56%, respectively). Kaplan-Meier survival curves showed that cervical length was the best discriminator of successful induction. CONCLUSION: Measurement of cervical length by transvaginal ultrasonography is a better predictor of success in labor induction with both topical prostaglandin and oxytocin.     

Failed induction of labor despite sequential prostaglandin E2 therapy

Preinduction cervical ripening with prostaglandin E2 (PGE2) is useful in minimizing the chances for a failed induction of labor. The lack of sufficient cervical dilation despite PGE2 and oxytocin therapy is uncommon. This investigation was undertaken to determine reasons for any failed inductions in pregnancies with pregel Bishop scores 4 or lower and requiring delivery within 24 hours. Fifteen (12.1%) of 124 eligible patients had failed inductions despite two 2.5 mg intravaginal doses. A finding in all the failures was a very unfavorable cervix (pregel Bishop score 0 to 2). The need for preterm delivery (33 to 37 weeks) was a common finding in the presence of a very unfavorable cervix. The data suggest that complicated pregnancies requiring delivery within 24 hours and failing to respond to sequential PGE2 therapy in the presence of a very unfavorable cervix may benefit from cesarean section without a prolonged induction.     

The labor induction: integrated clinical and sonographic variables that predict the outcome.

OBJECTIVE: To analyze the clinical and sonographic variables that predicts the success of labor induction. STUDY DESIGN: We studied the Bishop score, cervical length and parity in 196 pregnant women in the prediction of successful vaginal delivery within 24 h of induction. Logistic regression and segmentation analysis were performed. RESULTS: Cervical length (odds ratio (OR) 1.089, P<0.001), Bishop score (OR 0.751, P=0.001) and parity (OR 4.7, P<0.001) predict the success of labor induction. In a global analysis of the variables studied, the best statistic sequence that predicts the labor induction was found when we introduced parity in the first place. The success of labor induction in nulliparous was 50.8 and 83.3% in multiparous women (P=0.0001). CONCLUSIONS: Cervical length, Bishop score and parity, integrated in a flow chart, provide independent prediction of vaginal delivery within 24 h of induction.     

Induction of labor by using PGE2 and oxytocin in high risk pregnancies]

The study group consisted of 82 primigravid and 55 multiparous women with post term pregnancy, preeclampsia, intrauterine growth retardation, insufficiency of placenta and diabetes mellitus have induced labor. Prepidil (Upjohn) in dosage 0.5 mg was given into uterine cervix of 46 patients (PG group) and oxytocin was infused to 42 patients in dosage ranged from 5 mU/min to 30 mU/min (Ox group). Induction of labor has been considered as successful, if after 12 hours of drug administration, regular contractions of uterus and dilation of cervix more than 3 cm were obtained. Significant improvement of cervix state, measured by Bishop score has been observed only in PG group, even if the induction of labor failed. Similar rates of caesarean sections and the same occurrences of late and variable decelerations have been observed in both study groups. Results obtained in both these groups suggest that induction of labor in such pregnancies after prostaglandins administration is more effective than oxytocin infusion.     

Role of prostaglandin-induced cervical changes in labor induction

The role of the cervix in labor induction has been studied in a previous report. Cervical preparation by mechanical methods did not alter the course of induced labor. The same hypothesis is further elucidated in the present study using prostaglandin E2 vaginal suppositories for cervical preparation. Forty-seven pregnant women near term with Bishop scores of 4 or less were divided into three study groups: control subjects, oxytocin-treated patients, and prostaglandin group. A 12-hour preparation phase procedure was carried out to produce cervical and/or myometrial changes. All women had continuous measurement of uterine activity by an extraovular catheter. At the end of the preparation phase, the Bishop score was reevaluated, amniotomy carried out in all patients, and oxytocin infusion either started or continued. Although prostaglandin and oxytocin both significantly changed the cervix, oxytocin had the shortest induction-to-delivery interval, though the prostaglandin-treated group required lower concentrations of oxytocin. The authors conclude that with rigid control of Bishop score and timing of amniotomy and oxytocin infusion rates, prostaglandin-induced cervical changes alone did not uniquely benefit labor induction in the doses used, or within the time frame of the study.     

Comparison of ultrasonographic and digital cervical evaluation

Findings on ultrasound scanning of the cervix and lower uterine segment were compared with those on digital examination in patients in preterm labor or those in whom induction was planned. An ultrasound scoring system gave results that corresponded closely to those of the Bishop score.     

Predictive value of pelvic scores for induction of labor by local PGE2.

The predictive value of pelvic scores, parity, age and gestational age for induction of labor by local prostaglandin-E2 (PGE2) was examined in 336 women attempting induction of labor by intracervical or vaginal PGE2. The patient characteristics were correlated to: (1) vaginal delivery within 48 h, (2) the period from induction to onset of labor (latency period), and (3) the duration of labor. The Bishop score (P < 0.01) and even more the Lange score (P < 0.0001) were significantly inversely correlated to both latency period and induction-delivery period. This was caused by cervical dilatation (P < 0.001), fetal station (P < 0.05) and cervical length (P < 0.05), whereas position and consistency of the cervix were of no importance. All three periods studied were significantly (P < 0.0001) shorter in parous women. In primiparous women, gestational age was of no importance for the latency period; however, higher gestational age was associated with longer labor (P < 0.001). We conclude that the predictive value of pelvic scores on induction hardly differs using local PGE2 compared to conventional methods; furthermore, the Bishop score should be substituted, disregarding position and consistency of the cervix, but putting more weight to cervical dilatation. A new pelvic score is proposed.     

Digital and transvaginal ultrasound cervical assessment for prediction of successful labor induction.

OBJECTIVE: To compare the values of preinduction transvaginal cervical length measurements and Bishop score to predict successful labor induction. METHODS: A prospective, observational trial of nulliparous women undergoing labor induction. Inclusion criteria were gestational age between 36 and 42 weeks, singleton cephalic presentation of the fetus, and intact membranes. Preinduction cervical ripening was performed using 25 microg intravaginal misoprostol (PGE1), repeated every 4 h, up to a maximum of 3 doses. Induction was subsequently continued by oxytocin and amniotomy. RESULTS: A total of 43 women met the inclusion criteria. Mean preinduction cervical length for women with successful or failed labor induction was 26 mm (95% Confidence interval [CI], 27-32) and 34 mm (95% CI, 33-38), respectively (P=0.002). Mean Bishop scores for successful and failed induction groups were 5.4 (95% CI, 5.2-6.2) and 3.1 (95% CI, 2.8-3.5), respectively (P=0.003). CONCLUSION: Digital examination and transvaginal ultrasound of the cervix predict successful labor induction with reasonable accuracy.     

Intracervical misoprostol as an effective method of labor induction at term.

OBJECTS: The purpose of this study was to evaluate the safety and effectiveness of intracervical misoprostol for the induction of labor at term. METHODS: Eighty-nine term pregnancies requiring induction of labor were treated intracervically with 50 microg of misoprostol. The dose was repeated every 4 h until adequate uterine contraction and cervical dilatation were achieved. Status of cervical ripening, uterine contraction, cervical dilatation, labor course and side effects were recorded and analyzed. RESULTS: Among the 89 patients, 58 had an unfavorable cervix (Bishop score < or = 4) and 31 had a favorable cervix (Bishop score > 4). Labor was successfully induced in all cases, most (93.3%) of which required a single dose of misoprostol. Seventy-two patients (81%) proceeded to spontaneous vaginal delivery, and 61 (85%) deliveries were achieved within 12 h. The other 17 cases received cesarean delivery with indications of fetopelvic disproportion (six cases), failure of induction (seven cases) and acute fetal distress (four cases). The mean duration from induction to regular uterine contraction and to delivery was 483+/-537 min and 79.2+/-38.2 min, respectively, with no significant difference between the two groups with differing status of cervical ripening. Complications of uterine contraction, including tachysystole (15 cases), hypertonus (one case) and hyperstimulation (10 cases) were more common in the group of unfavorable cervix (45%) than that of favorable cervix (23%) (P < 0.05). CONCLUSION: In addition to the oral and intravaginal routes of administration, intracervical misoprostol at a single dose of 50 microg appears to be an effective method for induction of labor at term, but caution should be taken with cases with unfavorable cervix.     

Effect of vaginal pH on efficacy of misoprostol for cervical ripening and labor induction

OBJECTIVE: We sought to evaluate whether vaginal pH has an effect on the relative efficacy of misoprostol for cervical ripening and labor induction. STUDY DESIGN: Thirty-seven gravid women with an unfavorable cervix and indication for labor induction were enrolled in this prospective, double-blind, observational study. Baseline assessments of cervicovaginal pH and Bishop score were made at the time of enrollment by an independent examiner. All patients received 50 microg misoprostol intravaginally every 6 hours for 12 hours. After the initial 12 hours of preinduction, a repeat Bishop score assessment was made by the same initial examiner. Patients not in active labor at 12 hours were placed on a standardized oxytocin induction regimen. Labor was managed by the on-call obstetric team, who remained blinded to pH assessment. Clinical outcomes were evaluated. Statistical analyses were made by the Student t test, the Fisher exact test, and linear regression analysis. RESULTS: Average initial vaginal pH was 4.8 +/- 0.5 (range, 3.5-7.0) for the study cohort. No significant differences were noted between those patients with low vaginal pH (< or =4.5) compared with those with high pH vaginal (>4.5) with respect to maternal age, parity, gestational age, or initial Bishop score. Similarly, Bishop score change over preinduction interval (5.6 vs 4.9), time to active labor (16.3 vs 17. 1 hours), time to complete dilatation (20.0 vs 19.9 hours), and time to delivery (21.0 vs 21.6 hours) were not significantly different between the low and high pH groups, respectively. Linear regression analysis revealed no significant association between vaginal pH and Bishop score change during preinduction interval, time to active labor, time to complete dilatation, or time to delivery. CONCLUSION: Vaginal pH does not appear to influence the efficacy of intravaginally administered misoprostol for cervical ripening and labor induction.     

Foley尿管水囊促宫颈成熟用于足月妊娠引产的前瞻性随机对照研究

目的 比较Foley尿管水囊与普贝生栓促宫颈成熟用于足月妊娠引产的安全性和有效性. 方法 采用前瞻性随机对照研究方法,选择2009年6月至12月在本院待产的孕足月、单胎头位、有引产指征、阴道清洁度≤Ⅱ度、胎膜完整、官颈Bishop评分＜6分的初产妇,签署随机对照研究知情同意书后,随机分为2组,最终纳入分析的共126例,分别予Foley尿管水囊(64例)和普贝生栓(62例)促官颈成熟,Foley尿管水囊组与普贝生栓组孕妇的孕周、引产前宫颈评分、引产指征差异无统计学意义.采用t、x2检验或Fisher精确概率法比较2组孕妇的引产成功率、分娩方式、产程时间及母儿结局. 结果 Foley尿管水囊组与普贝生栓组宫颈评分改善、引产成功率、阴道分娩率、总产程、产后出血量差异均无统计学意义(P＞0.05).Foley尿管水囊组较普贝生栓组引产24 h内阴道分娩率低[28.1％(18/64)与56.5％(35/62),t=10.37,P＜0.05],宫缩过频过强发生率也较低[0.0％(0/64)与17.7％(11/62),P＜0.05],但缩宫素使用率高[87.5％(56/64)与21.0％(13/62),x2 =56.27,P＜0.05].2组新生儿Apgar评分、羊水胎粪污染发生率、新生儿体重差异均无统计学意义(P＞0.05).2组孕妇无一例发生产褥感染. 结论 严格掌握Foley尿管水囊促宫颈成熟的指征及执行无菌操作规程,可以取得与普贝生栓相似的促官颈成熟效果及引产母婴结局,未发生过频过强官缩,具有安全性高及成本低廉等优点.     

Comparison of the Bishop score, body mass index and transvaginal cervical length in predicting the success of labor induction

Purpose  To evaluate the role of ultrasonographic and various maternal and fetal parameters in predicting successful labor induction. Methods  Body mass index, cervical length, dilatation, effacement, Bishop score, parity, maternal age and birth weight were evaluated in 189 singleton pregnant women at 37–42 weeks of gestation and having induction of labor. All underwent induction of labor with oxytocin. Body mass index was calculated using the formula weight (kg)/height² (m), cervical measurement was performed by transvaginal ultrasonography and Bishop score was determined by digital examination of cervix. Results  Logistic regression analysis indicated that the cervical length and body mass index were independent variables in determining the risk of cesarean section (OR = 1.206, P = 0.000, CI 95% = 1.117–1.303; OR = 1.223, P = 0.007, CI 95% = 1.058–1.414 respectively). In multiple linear regression analysis, the effect of cervical length and body mass index on induction delivery interval was found to be statistically significant (t = 5.738, P = 0.000; t = 2.680, P = 0.009, respectively). ROC curve showed that the best parameter in predicting the risk of cesarean section was cervical length and that cervical length and body mass index were better parameters compared to the Bishop score (the areas under the curve are 0.819, 0.701 and 0.416, respectively). Conclusions  Body mass index and transvaginal cervical length were better predictors compared to the Bishop score in determining the success of labor induction.