Induction implies stimulation of contractions before the spontaneous onset of labor, with or without ruptured membranes. Augmentation refers to stimulation of spontaneous contractions that are considered inadequate because of failed cervical dilation and fetal descent. According to the National Center for Health Statistics, the incidence of labor induction in the United States more than doubled from 9.5 percent in 1991 to 22.5 percent in 2006 (Martin and associates, 2009). The incidence is variable between practices. For example, 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 about 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, as well as a description of various techniques to effect pre-induction cervical ripening.
Induction is indicated when the benefits to either mother or fetus outweigh those of continuing the pregnancy. Indications include immediate conditions such as ruptured membranes with chorioamnionitis or severe preeclampsia. The more common indications include membrane rupture without labor, gestational hypertension, nonreassuring fetal status, postterm pregnancy, and various maternal medical conditions such as chronic hypertension and diabetes (American College of Obstetricians and Gynecologists, 1999a).
There are a number of techniques available to induce or augment labor, and these are discussed separately. Importantly, and as recommended in Guidelines for Perinatal Care, each obstetrical department should have its own written protocols that describe administration of oxytocin and other uterotonics (American Academy of Pediatrics and American College of Obstetricians and Gynecologists, 2007).
Contraindications to induction are similar to those that preclude spontaneous labor or delivery. Fetal factors include appreciable macrosomia, multifetal gestation, severe hydrocephalus, malpresentation, or nonreassuring fetal status. The few maternal contraindications are related to prior uterine incision type, contracted or distorted pelvic anatomy, abnormal placentation, and conditions such as active genital herpes infection or cervical cancer.
Maternal complication rates that are increased in association with labor induction include cesarean delivery, chorioamnionitis, and uterine atony.
This is especially increased in nulliparas undergoing induction (Luthy and colleagues, 2004; Yeast and associates, 1999). A number of investigators have reported two- to threefold risks (Hoffman and Sciscione, 2003; Maslow and Sweeny, 2000; Smith and colleagues, 2003). Moreover, these rates are inversely related with favorability of the cervix at induction, that is, the Bishop score (Vahratian and colleagues, 2005; Vrouenraets and associates, 2005).
However, pre-induction cervical ripening may not lower the cesarean delivery rate in a nullipara with an unfavorable cervix (Mercer, 2005). In a retrospective cohort study, Hamar and associates (2001) found that the rate of cesarean delivery following elective induction was ...