Post-term pregnancy is the most commonly cited indication for labor induction. Data from several large multicenter randomized studies have reported favorable outcomes with routine induction as early as 41 weeks. One of the largest studies included 3407 low-risk women randomized at 41 weeks to expectant management versus labor induction. A significantly lower cesarean rate was noted in the electively induced group, 21.2% versus 24.5%, a difference thought to be due to fewer cesareans performed for nonreassuring fetal heart rate tracings [1]. While a review of 19 studies investigating routine labor induction after 41 weeks found no difference in the cesarean delivery rate, a lower rate of perinatal mortality was noted. Additionally, no effect was seen in the instrumental delivery rate, use of analgesia or incidence of fetal heart rate abnormalities [2]. In a report describing the changing patterns in labor induction, the average gestational age at induction for the indication of post-term pregnancy was noted to have declined from 41.9 weeks to 41 weeks [3].

Other indications for proceeding with labor induction include pre-eclampsia, eclampsia, abruptio placentae, chorio-amnionitis, fetal demise, premature rupture of membranes, isoimmunization, fetal growth restriction, and maternal medical conditions such as diabetes and chronic hypertension.

Additionally, elective inductions for logistic or psychosocial reasons have become more common. There has been at least a 15-fold rise in the number of elective inductions since 1990. While benefits cited for initiating an elective induction include avoiding a rapid delivery away from the hospital and minimizing any disruption to the patient’s and provider’s work and nonwork responsibilities, risks include increased iatrogenic prematurity, increased healthcare costs, and increased rates of operative delivery [4]. The greatest risk appears to involve elective induction of nulliparous patients, particularly those with an unfavorable cervix. In an investigation comparing 7683 nulliparous women who were electively induced to a matched cohort of 7683 nulliparous women who had spontaneous labors, the electively induced group had higher rates of cesarean delivery (10% vs 7%), instrumental delivery (32% vs 29%), and use of epidural anesthesia (80% vs 58%). Similar findings were reported in other studies with all showing an approximate twofold increased risk of cesarean delivery.

Prior to initiating a labor induction for logistic or psychosocial indications, the American College of Obstetricians and Gynecologists suggests that fetal lung maturity be established or one of the following criteria met: fetal heart tones have been documented for 20 weeks by nonelectronic fetoscopy or for 30 weeks by Doppler; it has been 36 weeks since a positive serum or urine human chorionic gonadotropin pregnancy test was performed by a reliable lab; an ultrasound measurement of the crown–rump length, obtained at 6–12 weeks, supports a gestational age of at least 39 weeks; or an ultrasound obtained at 13–20 weeks confirms the gestational age of at least 39 weeks determined by clinical history and physical examination [5].

Contraindications to labor induction include: prior classic uterine incision, active genital herpes infection, placenta or vasa previa, and transverse fetal lie. There are other conditions which are not necessarily contraindications, but caution and judgment should be exercised when managing them. These include: multiple gestation, maternal cardiac disease, grand multiparity, breech presentation, abnormal fetal heart rate patterns that do not require immediate delivery, and severe hypertension.

Before beginning a labor induction, the risks, alternatives, and potential need for cesarean delivery should be thoroughly discussed with the patient. Additionally, the following should be completed: a review of the gestational age; estimation of the fetal size and position; and assessment of the patient’s pelvis and cervical status. The Bishop score is the method most commonly used to assess the cervix. It was originally developed to describe the state of multiparous cervices prior to the onset of spontaneous labor. Four characteristics of the cervical exam are used to tabulate a Bishop score: effacement, dilation, consistency, and position. In 1966, Friedman studied the Bishop score of 408 multiparous patients before labor, many of which were elective inductions. Labor induction was successful in all patients with a Bishop score of 9 or greater while 20% of inductions failed in patients with a Bishop score of 4 or less. A score between 5 and 8 resulted in a 4.8% failure rate. Investigators have demonstrated that cervical dilation is the most important component of the Bishop score in predicting success of a labor induction. Effacement, station and consistency were found to have about half of the influence while position had little effect as compared with cervical dilation.