In low-risk pregnancies, does inducing labor at or beyond term improve maternal or neonatal outcomes?
Fetal or neonatal deaths in women who delivered after their due date and before 42 weeks occur at a rate of less than 0.5 percent, regardless of whether labor is induced or spontaneous. Compared with awaiting spontaneous labor, inducing labor between 41 and 42 weeks is associated with fewer perinatal deaths and fewer cases of meconium aspiration. However, there were no differences in admissions to the neonatal intensive care unit (NICU). Induction beyond term does not increase rates of cesarean delivery.
Postterm delivery beyond 42 weeks' gestation poses risks to mothers and babies, including increased perinatal death, increased cesarean deliveries, perineal injuries from macrosomia, and labor dystocias. Physicians have turned to induction of labor or antenatal surveillance as a means of preventing complications.1
This Cochrane review included randomized controlled trials (RCTs) comparing induction of low-risk pregnant women at a predetermined gestational age versus expectant management until an indication for delivery arose. A variety of neonatal, maternal, and health service use outcomes were reported. Nineteen RCTs that included a total of 7,984 women were included and analyzed in three groups of trials, in which labor was induced at 37 to 40 completed weeks, 41 completed weeks, and 42 completed weeks.
For the outcome of perinatal death, no significant difference was noted between induction and expectant groups in any of the individual gestational age categories. However, if the results from groups induced at 41 and 42 completed weeks were combined, there was a significant reduction in fetal and neonatal deaths, and fewer cases of meconium aspiration syndrome occurred in studies when labor was induced at either 41 or 42 weeks. However, there was no significant difference in NICU admissions. In no category of studies was there a significant difference in the rate of cesarean delivery between induction and expectant management.
Data reviewed here can guide patient counseling on the magnitude of risks involved with induction or awaiting labor. The evidence favors induction between 41 and 42 weeks to reduce perinatal mortality and meconium aspiration, but the absolute risk of these outcomes is small. In the combined category of induction at 41 or 42 weeks, one out of 2,986 newborns in the induction group and nine out of 2,953 in the spontaneous labor group died. Because there is no increased risk of cesarean delivery rates, instrumented deliveries, use of analgesia, or abnormalities in fetal heart rate tracings, the disadvantages of induction are small. In light of these findings, the American College of Obstetricians and Gynecologists (ACOG) recommends that women with postterm gestations who have unfavorable cervices can undergo labor induction or be managed expectantly, but they acknowledge that many physicians routinely induce labor by 42 weeks. There is no evidence regarding the effectiveness of antenatal testing in women who are postterm. However, based on expert consensus, ACOG recommends a nonstress test and amniotic fluid index twice weekly, starting at 41 weeks.1
There is not strong evidence to determine the exact optimal timing of induction between 41 and 42 weeks' gestation. In clinical practice, the decision between induction and expectant management should include favorability of the cervix, maternal parity, and patient preferences, and often includes patient or physician convenience.