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Introduction

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Induction implies stimulation of contractions before the spontaneous onset of labor, with or without ruptured membranes. When the cervix is closed and uneffaced, labor induction will often commence with cervical ripening, a process that generally employs prostaglandins to soften and open the cervix.

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Augmentation refers to enhancement of spontaneous contractions that are considered inadequate because of failed cervical dilation and fetal descent. In the United States, the incidence of labor induction more than doubled from 9.5 percent in 1991 to 23.2 percent in 2011 (Martin, 2013). The incidence is variable between practices. At Parkland Hospital approximately 35 percent of labors are induced or augmented. By comparison, at the University of Alabama at Birmingham Hospital, labor is induced in approximately 20 percent of women, and another 35 percent are given oxytocin for augmentation—a total of 55 percent. This chapter includes an overview of indications for labor induction and augmentation and a description of various techniques to effect preinduction cervical ripening.

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Labor Induction

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Indications
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Induction is indicated when the benefits to either mother or fetus outweigh those of pregnancy continuation. The more common indications include membrane rupture without labor, gestational hypertension, oligohydramnios, nonreassuring fetal status, postterm pregnancy, and various maternal medical conditions such as chronic hypertension and diabetes (American College of Obstetricians and Gynecologists, 2013b).

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Contraindications
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Methods to induce or augment labor are contraindicated by most conditions that preclude spontaneous labor or delivery. The few maternal contraindications are related to prior uterine incision type, contracted or distorted pelvic anatomy, abnormally implanted placentas, and uncommon conditions such as active genital herpes infection or cervical cancer. Fetal factors include appreciable macrosomia, severe hydrocephalus, malpresentation, or nonreassuring fetal status.

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Techniques
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Oxytocin has been used for decades to induce or augment labor. Other effective methods include prostaglandins, such as misoprostol and dinoprostone, and mechanical methods that encompass stripping of membranes, artificial rupture of membranes, extraamnionic saline infusion, transcervical balloons, and hygroscopic cervical dilators. Importantly, and as recommended in Guidelines for Perinatal Care, each obstetrical department should have its own written protocols that describe administration of these methods for labor induction and augmentation (American Academy of Pediatrics and American College of Obstetricians and Gynecologists, 2012).

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Risks
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Maternal complications associated with labor induction consist of cesarean delivery, chorioamnionitis, uterine scar rupture, and postpartum hemorrhage from uterine atony.

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Cesarean Delivery Rate
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This is especially increased in nulliparas undergoing induction (Luthy, 2004; Yeast, 1999). Indeed, several investigators have reported a two- to threefold increased risk (Hoffman, 2003; Maslow, 2000; Smith, 2003). Moreover, these rates are inversely related with cervical favorability at induction, that is, the Bishop score (Vahratian, 2005; Vrouenraets, 2005). The ...

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