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

OBJECTIVE: The objective of this review was to identify, assess and synthesize the best available evidence on the effects of induction prior to post-term on the mother and fetus. Maternal and fetal outcomes after routine labor induction in low-risk pregnancies at 41+0 to 41+6 gestational weeks (prior to post-term) were compared to routine labor induction at 42+0 to 42+6 gestational weeks (post-term). INTRODUCTION: Induction of labor when a pregnancy exceeds 14 days past the estimated due date has long been used as an intervention to prevent adverse fetal and maternal outcomes. Over the last decade, clinical procedures have changed in many countries towards earlier induction. A shift towards earlier inductions may lead to 15–20% more inductions. Given the fact that induction as an intervention can cause harm to both mother and child, it is essential to ensure that the benefits of the change in clinical practice outweigh the harms. INCLUSION CRITERIA: This review included studies with participants with expected low-risk deliveries, where both fetus and mother were considered healthy at inclusion and with no known risks besides the potential risk of the ongoing pregnancy. Included studies evaluated induction at 41+1–6 gestational weeks compared to 42+1–6 gestational weeks. Randomized control trials (n = 2), quasi-experimental trials (n = 2), and cohort studies (n = 3) were included. The primary outcomes of interest were cesarean section, instrumental vaginal delivery, low Apgar score (≤ 7/5 min.), and low pH (< 7.10). Secondary outcomes included additional indicators of fetal or maternal wellbeing related to prolonged pregnancy or induction. METHODS: The following information sources were searched for published and unpublished studies: PubMed, CINAHL, Embase, Scopus, Swemed+, POPLINE; Cochrane, TRIP; Current Controlled Trials; Web of Science, and, for gray literature: MedNar; Google Scholar, ProQuest Nursing & Allied Health Source, and guidelines from the Royal College of Obstetricians and Gynaecologists, and American College of Obstetricians and Gynecologists, according to the published protocol. In addition, OpenGrey and guidelines from the National Institute for Health and Care Excellence, World Health Organization, and Society of Obstetricians and Gynaecologists of Canada were sought. Included papers were assessed by all three reviewers independently using the Joanna Briggs Institute System for the Unified Management, Assessment and Review of Information (JBI SUMARI). The standardized data extraction tool from JBI SUMARI was used. Data were pooled in a statistical meta-analysis model using RevMan 5, when the criteria for meta-analysis were met. Non-pooled results were presented separately. RESULTS: Induction at 41+0–6 gestational weeks compared to 42+0–6 gestational weeks was found to be associated with an increased risk of overall 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 1.45–5.2), uterine rupture (RR = 1.97, 95% CI 1.54–2.52), pH < 7.10 (RR = 1.9, 95% CI 1.48–2.43), and a decreased risk of oligohydramnios (RR = 0.4, 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. No differences were seen for postpartum hemorrhage, shoulder dystocia, meconium aspiration, 5-minute Apgar score < 7, or admission to neonatal intensive care unit. A policy of awaiting spontaneous onset of labor until 42+0–6 gestational weeks showed, that approximately 70% went into spontaneous labor. CONCLUSIONS: Induction prior to post-term was associated with few beneficial outcomes and several adverse outcomes. This draws attention to possible iatrogenic effects affecting large numbers of low-risk women in contemporary maternity care. According to the World Health Organization, expected benefits from a medical intervention must outweigh potential harms. Hence, our results do not support the widespread use of routine induction prior to post-term (41+0–6 gestational weeks).