In other cases, if interference becomes imperative, the introduction of a bougie into the uterus, or the employment of a small Champetier de Ribes rubber bag acts as an effective uterine irritant and brings about complete dilatation.
—J. Whitridge Williams (1903)
No effective means of labor induction were available when Williams wrote the first edition of this book. Labor augmentation methods were largely ineffective, and manual cervical dilation was performed as a last resort. Contrast with today, when several pharmacological agents permit labor induction or augmentation, and ironically the use of a “bougie” has come back into vogue.
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. Augmentation refers to enhancement of spontaneous contractions that are considered inadequate because of failed cervical dilation and fetal descent—inertia uteri—as described by Williams (1903).
In the United States, the incidence of labor induction rose 2.5-fold from 9.5 percent in 1991 to 23.8 percent in 2015 (Martin, 2017). The incidence varies 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 discusses indications for labor induction and augmentation and various techniques to effect preinduction cervical ripening.
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, 2016).
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.
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 membrane stripping, 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, 2017).