Influence of labor induction on obstetric outcomes in patients with prolonged pregnancy: a comparison between elective labor induction and spontaneous onset of labor beyond term

Background: Prolonged pregnancy is the most frequent reason for induction of labor. This study aims to determine the effects of labor induction on delivery outcome and to quantify the risks of cesarean delivery associated with labor induction in post-date pregnancies. Patients and methods: This retrospective case-control study included a total of 205 women who reached 42 weeks' gestation (41 weeks and 3 days) between January 2002 and April 2004 and who were scheduled for induction of labor with vaginal prostaglandins. These cases were matched for age and parity with controls in spontaneous labor beyond 41 weeks' gestation. Women with any additional medical or obstetric risk factors were excluded from the study. Maternal, neonatal and delivery outcomes were the main variables of interest. Results: During the study period the data of 410 women were available for analysis. Our data revealed that the use of amniotomy (p = 0.02), oxytocin (p = 0.006) and epidural analgesia (p = 0.001) was increased significantly in the induction group compared with the control group of women with spontaneous onset of labor beyond term. The frequency of cesarean delivery and vacuum extraction was also significantly higher in the induction group (p = 0.0001). The Bishop score before induction was an important factor that affected the delivery outcome, resulting in significantly higher rates of cesarean section and vacuum extraction when the score was unfavorable (p = 0.0001). A univariate regression model revealed induction per se (p = 0.0001), primiparity (p = 0.0001), increased maternal age (p = 0.006) and an unfavorable Bishop score (p = 0.0001) as statistically significant risk factors for cesarean section. In a multivariate logistic regression model, primiparity (p = 0.03), increased maternal age (p = 0.02) and an unfavorable Bishop score (p = 0.01) remained independent risk factors for cesarean section. High infant birth weight was also an independent risk factor (p = 0.03). Conclusions: Our data suggest that women undergoing labor induction because of prolonged pregnancy should be sufficiently informed regarding the risks of a cesarean section or a vacuum extraction. Furthermore, the option of elective cesarean section should be considered, particularly in primiparous women with an unfavorable cervix, higher age, and high estimated infant birth weight.