12 hours of uterine stimulation with oxytocin after membrane rupture, whereas Kawakita and coworkers (2016) recommend up to 15 hours for multiparas.
As discussed, the condition of the cervix-described as cervical "ripeness" or "favorability"-is important to successful labor induction. However, at least some estimates of favorability are highly subjective (Peltovich, 2017). hat said, pharmacological and mechanical methods can enhance cervical favorabilityalso termed preinduction cervical ripening.
Some of the techniques described may have benefits when compared with oxytocin induction alone (Table
Some are also quite successful for initiating labor. However, few data support the premise that any of these techniques lower cesarean delivery rates or lessen maternal or neonatal morbidity compared with women in whom these methods are not used.
One quantifiable method used to predict labor induction outcomes is the score described by Bishop (1964) and presented in
Table 26-2. As favorability or Bishop score declines, the rate of induction to efect vaginal delivery also decreases. A Bishop score of 9 conveys a high likelihood for a successful induction. Por research purposes, a Bishop score of 4 or less identifies an unfavorable cervix and may be an indication for cervical ripening.
TABLE 26-2. Bishop Scoring System Used for Assessment of Inducibility
Score Dilatation (cm) Efacement (%) Station (-3 to +2) Consistency Position �80 +1, +2
From Bishop, 1964.
Laughon and coworkers (201i1) attempted to simpliy the Bishop score by performing a regression analysis on 5610 singleton, uncomplicated deliveries between 37°/7 and 416/7 weeks' gestation in nulliparas. Only cervical dilation, station, and efacement were signiicantly associated with successful vaginal delivery. hus, a simplified Bishop score, which incorporated only these three parameters, had a similar or improved positiveor negative-predictive value compared with that of the original Bishop score. Other investigators have reported similar findings when consistency and position are omitted (Ivars, 2016; Raghuraman,i2016).
Transvaginal sonographic measurement of cervical length is the only biophysical marker that has been evaluated as a Bishop score alternative (Feltovich, 2017). In one metaanalysis of trials in which cervical length was used to predict successful induction, study criteria heterogeneity precluded the authors from reaching a summary answer (Hatfield, 2007). A subsequent metaanalysis of 31 trials found overall low sensitivity and speciicity and limited predictive utility for sonographic cervical length and "wedging" to predict successful labor induction (Verhoeven, 2013).
Unfortunately, women frequently have an indication for induction but also have an unfavorable cervix. Several techniques are available, and these can also stimulate contractions and thereby aid subsequent labor induction or augmentation. Methods most commonly used for preinduction cervical ripening and induction include several prostaglandin analogues.
Dinoprostone is a synthetic analogue of prostaglandin E2 (PGE2). It is commercially available in three forms: a gel, a timerelease vaginal insert, and a 20-mg suppository (Table 26-1). he gel and time-release vaginal insert formulations are indicated only for cervical ripening before labor induction. However, the 20-mg suppository is not indicated for cervical ripening. It instead is used for pregnancy termination between 12 and 20 weeks' gestation and for evacuation of the uterus after fetal demise up to 28 weeks.