Labor induction has primarily been efected with the use of amniotomy, prostaglandins, and oxytocin, alone or in combination. Because preinduction cervical ripening frequently eventuates in labor, studies to determine induction eicacy for some of these agents have produced sometimes confusing results. he use of prostaglandins for labor augmentation has generally been considered experimental due to their high rates of uterine tachysystole.
• Prostaglandin E,
Both vaginal and oral misoprostol are used for either cervical ripening or labor induction. For labor induction in women at or near term with either prematurely ruptured membranes or a favorable cervix, 100 I1g of oral or 25 1g of vaginal misoprostol has similar eicacy compared with intravenous oxytocin. From these studies, evidence supports that oral misoprostol may be superior (Alirevic, 2014; Hofmeyr, 2010; Lo, 2003). Misoprostol may be associated with a greater rate of uterine tachysystole, particularly at higher doses. Also, induction with PGEI may prove inefective and require subsequent induction or augmentation with oxtocin. hus, although there are trade-ofs regarding the risks, costs, and ease of administration of each drug, either is suitable for labor induction. At Parkland Hospital, we administer an initial oral 100-l1g dose, which may be repeated ater 6 hours for inadequate labor. Six hours ater the second dose or in those with tachysystole, an oxytocin infusion is begun, if needed, for hypotonic labor. Dobert and colleagues (2017) have described preliminary use of a misoprostol vaginal insert.
For labor aumentation, results of a randomized controlled trial showed oral misoprostol, 75 ILg given at 4-hour intervals for a maximum of two doses, to be safe and efective (Bleich, 2011). he 75-Lg dose was based on a previous dose-inding study (Villano, 2011). Although there was more uterine tachy systole among women with labor augmented with misoprostol, the frequency of nonreassuring fetal status or cesarean delivery did not difer between oxytocin and misoprostol.
In many instances, preinduction cervical ripening and labor induction are simply a continuum. hus, "ripening" can also stimulate labor. If not, induction or augmentation may be continued with solutions of oxytocin given by infusion pump. Its use in augmentation is a key component in the active management oflabor, described in Chapter 22 (p. 438). With oxytocin use, the American College of Obstetricians and Gynecologists (2016) recommends fetal heart rate and uterine contraction monitoring. Contractions can be monitored either by palpation or by electronic means.
he goal of induction or augmentation is to efect uterine activity suicient to produce cervical change and fetal descent, while avoiding development of a nonreassuring fetal status. In general, oxytocin is discontinued if the number of contractions persists with a frequency of more than ive in a 10-minute period or more than seven in a 15-minute period or with a persistent nonreassuring fetal heart rate pattern. Oxytocin discontinuation nearly always rapidly lowers contraction frequency. When oxytocin is stopped, its concentration in plasma rapidly falls because the half-life is approximately 3 to 5 minutes. Seitchik and associates (1984) found that the uterus contracts within 3 to 5 minutes of beginning an oxytocin infusion and that a plasma steady state is reached in 40 minutes. Response is highly variable and depends on preexisting uterine activity, cervical status, pregnancy duration, and individual biological diferences. Caldeyro-Barcia and Poseiro (1960) reported that the uterine response to oxytocin increases from 20 to 30 weeks' gestation and rises rapidly at term (Chap. 24, p. 479).