Are there adverse maternal and neonatal outcomes associated with induction of labor when there is no well-accepted indication?

BACKGROUND: Elective inductions without a clear medical or obstetric indication are increasingly common. There are multiple studies suggesting that elective induction increases the risk of cesarean and instrumental delivery. However, the data are inconsistent, and many of the studies were performed before the introduction of cervical ripening agents. Therefore, it is unclear whether elective inductions without a medical or obstetric indication increase the risk of adverse outcomes under current practice guidelines.

POPULATION STUDIED: A sample of 2886 low-risk obstetric patients who underwent induction of labor without a medical or obstetric indication were compared with 9648 women with spontaneous labor. Eligibility criteria included women with single fetuses in a vertex position who delivered in the hospital between 37 and 41 weeks’ gestation. Women were excluded if an indication for induction was present according to the 1996 American College of Obstetrics and Gynecology (ACOG) guidelines. Of note, women who underwent induction for suspected macrosomia or post-term pregnancy before 42 weeks were not excluded from the study. The 2 populations of women were similar in most characteristics; however, those in the induction group were more likely to have a gestational age of 41 weeks or more (30% vs 18%), to have an infant with a birth weight of 4000 g or more (21.7% vs 13.3%), and to have medical insurance.

STUDY DESIGN AND VALIDITY: A sample of births in Washington State from 1989 to 1993 was obtained using birth certificates and linked hospital discharge data. Procedure codes and International Classification of Diseases—ninth revision codes used during the birth hospitalization were analyzed to determine whether a medical or obstetric indication for induction of labor was present. A random sample of women who underwent induction was compared with a random sample of women with spontaneous onset of labor. The retrospective cohort model was an appropriate design for this study. However, birth certificates and discharge data are often not complete with reference to the full hospitalization record. Because the charts from the birth hospitalization were not reviewed, a misclassification bias may have occurred. In addition, there are often unmeasured characteristics that influence the decision to induce labor that are not recorded on birth certificates or discharge data.

OUTCOMES MEASURED: The primary outcomes measured were the risk of cesarean or instrumental delivery (forceps or vacuum extraction) associated with elective induction of labor compared with spontaneous onset of labor. Other outcomes measured were risk of birth injury, 5-minute APGAR score less than 7, presence of meconium, and meconium aspiration.

RESULTS: Among women meeting the study eligibility criteria, the proportion of births by induction nearly doubled during the study period (10.2% in 1989 to 19.7% in 1993). Nulliparous women who were induced were more likely to have a cesarean delivery than those women with spontaneous onset of labor (19.4% vs 9.9%; relative risk [RR, adjusted for birth weight]=1.77; 95% confidence interval [CI], 1.50-2.08; number needed to harm [NNH]=11). For multiparous women there was no difference in cesarean delivery rate (4% in each group). The risk of instrumental vaginal delivery was slightly increased for women with induced labor (18.6% vs 15.5%; RR=1.20; 95% CI, 1.09-1.36; NNH=32). There was also an increase in the incidence of shoulder dystocia in the induction group (3% vs 1.7%; RR=1.32; 95% CI, 1.02-1.69). Of the other outcomes, the only difference between the groups was a decreased risk of moderate to heavy meconium present at birth in the induction group (4.4% vs 5.7%; RR=0.78; 95% CI, 0.65-0.95). However, this was not associated with a decreased risk of meconium aspiration. As these differences could potentially be confounded by a post-term gestation of 41 weeks or more, the authors repeated a data analysis including only women who delivered between 37 and 41 weeks. All outcomes were unchanged.