Efforts continue to reduce the rate of cesarean deliveries in the United States from the peak of 24.7 percent in 1988. In 1996, the rate was 20.7 percent. Although induction of labor for medical indications is clearly associated with an increased rate of cesarean delivery, the risk associated with elective induction of labor remains unclear, and the practice of labor induction continues to increase. Seyb and colleagues studied all nulliparous women admitted to the delivery unit of a university hospital to establish the rates of cesarean delivery associated with induction of labor for elective and medical indications.

The study was restricted to nulliparous women with a singleton, vertex presentation at 37 or more weeks of gestation. Medical indications for induction of labor in 294 women included gestation greater than 41 weeks, preeclampsia, hypertension, diabetes, fetal growth restriction and premature rupture of membranes. Elective induction was chosen for 143 women for a variety of reasons, mainly favorable cervix at term or suspected problems in fetal growth. The remaining 1,124 women in spontaneous labor provided a baseline rate of cesarean delivery. Physicians and nurse-midwives made all clinical decisions in accordance with the usual practices on the unit.

Women undergoing elective labor induction were more likely to be older and white, and to have a private obstetrician than other women in the study. They also had higher rates of epidural analgesia (94.4 percent compared with 79.4 percent for spontaneous labor and 89.1 percent for medical induction of labor) and higher mean birth weights. In the spontaneous labor group, the cesarean delivery rate was 7.8 percent. The rates for medical and elective labor induction were 17.7 and 17.5 percent, respectively.

Besides induction, other factors associated with increased risk of cesarean delivery were maternal body mass index greater than 26 kg per m², gestational age of 40 or more weeks, birth weight of 4,000 g (8 lb, 12 oz) or more, premature rupture of membranes, use of epidural analgesia and chorioamnionitis. Use of induction remained significant when all variables were controlled in the analysis. Induction of labor was also associated with significant increases in duration of stay in the delivery unit and in postpartum hospital stay. The groups did not differ in postpartum complications or neonatal outcomes. Total costs for elective and medical induction of labor increased 17.4 and 29.1 percent, respectively.

The authors conclude that elective induction of labor is an important risk factor for cesarean delivery in nulliparous women. In addition to the increased delivery costs, future pregnancies are likely to be more complicated and expensive because of the primary cesarean delivery. They recommend avoiding elective induction of labor in cases of unproven benefit as a major strategy to decrease the cesarean delivery rate.