Effects of induction of labor prior to post-term in low-risk pregnancies: a systematic review

Background Existing systematic reviews on labor induction may use too loose inclusion criteria to actually reflect contemporary practice and/or inappropriate comparison group definitions, e.g. regarding gestational age criteria. If their conclusions form the evidence base for clinical guidelines, recent changes in obstetric practice towards earlier induction in low-risk pregnancies may be based on false conclusions. For example, some reviews include studies, where the expectant management group can continue pregnancy up to 3-4 weeks after estimated due date. We identified, assessed, and synthesized the best available evidence on maternal/fetal effects of routine labor induction in low-risk pregnancies at 41+0-6 vs. 42+0-6 gestational weeks. Method We conducted a metaanalysis on 7 original studies selected from strict criteria on (1) pregnancy duration in comparison groups, (2) methods for due date estimation, and (3) timeliness. We presented preliminary findings in Gothenburg 2016. In Iceland, we will give a brief summary of main results, demonstrate methodological problems in existing evidence, and suggest a new model for defining comparison groups in studies on routine labor induction. Findings Compared to expectant management, induction prior to post-term was associated with an increased risk of cesarean section (relative risk (RR) 1.11, 95% confidence interval (CI) 1.09-1.14), cesarean section due to failure to progress (RR 1.43, 95% CI 1.01-2.01), chorioamnionitis (RR 1,13; 95% CI 1.05-1.21), labor dystocia (RR 1.29, 95% CI 1.22-1.37), precipitate labor (RR 2.75, 95% CI 1.45-5.20), uterine rupture (RR 1.97, 95% CI 1.54-2.52), pH < 7.10 (RR 1.90, 95% CI 1.48-2.43), and a decreased risk of oligohydramnios (RR 0.40, 95% CI 0.24-0.67), and meconium stained amniotic fluid (RR 0.82, 95% CI 0.75-0.91). Data lacked statistical power to draw conclusions on perinatal death. Conclusion Our findings do not support the widespread use of routine induction prior to post-term. We argue that appropriate inclusion criteria are critical for obtaining relevant conclusions.