The induction of labor (IOL) is a cornerstone of modern obstetric practice, aimed at artificially initiating uterine contractions before the spontaneous onset of labor to achieve vaginal delivery. While historically reserved for medical or fetal indications, elective induction—particularly in low-risk pregnancies—has emerged as a topic of significant clinical interest and debate. The decision to induce labor in an otherwise uncomplicated pregnancy must balance maternal and neonatal outcomes, healthcare resource utilization, and patient preferences [1]. Traditionally, concerns surrounding elective IOL included the potential for increased rates of caesarean delivery, longer labor duration, and heightened maternal or neonatal complications. These concerns were largely based on older observational studies that compared outcomes of induced labor to spontaneous labor, which introduced comparator bias and limited clinical applicability. However, evolving evidence has challenged these longstanding beliefs, particularly regarding induction at 39 weeks of gestation in low-risk nulliparous women. A pivotal moment in this discourse was the publication of the ARRIVE trial (A Randomized Trial of Induction Versus Expectant Management), a large multicentre randomized controlled trial involving over 6,000 low-risk nulliparous women [2]. The trial demonstrated that elective induction at 39 weeks was associated with a significantly lower caesarean rate (18.6% vs. 22.2%), a reduction in hypertensive disorders, and no increase in adverse neonatal outcomes compared to expectant management. Importantly, these findings contradicted prior assumptions and suggested a protective rather than detrimental effect of induction in this specific population. Complementary evidence from large-scale cohort studies, including those by Cheng et al. and Darney et al., reinforced these findings [3] [4]. Elective induction at 39 weeks was associated with reduced maternal and neonatal morbidity compared to expectant management. Systematic reviews, including that by Caughey et al., similarly concluded that elective induction, particularly at or beyond 41 weeks, might reduce caesarean rates and improve neonatal outcomes, though data for 39 weeks was historically sparse and less definitive [5]. Despite the strength of these findings, concerns remain regarding the generalizability of trial data to real-world clinical settings, particularly those with variable adherence to labor protocols or limited resources. Moreover, professional societies such as the Society for Maternal-Fetal Medicine (SMFM) and American College of Nurse-Midwives (ACNM) have advised cautious implementation, emphasizing the need for shared decision-making and appropriate infrastructure [6]. In light of this evolving evidence base, the concept of 39 weeks as a new benchmark for delivery timing in low-risk pregnancies is gaining traction. It challenges traditional norms that equate 40 weeks with “term” and redefines what may be considered the safest window for delivery. Aim of the Review This review article critically examines the current literature surrounding elective induction of labor in low-risk pregnancies beyond 39 weeks, synthesizing data from randomized trials, systematic reviews, and observational studies. It aims to provide an evidence-based rationale in favor of elective IOL at 39 weeks, while addressing concerns around safety, feasibility, and applicability in diverse clinical settings. By integrating clinical outcomes with epidemiologic insights, the article explores the central question: Is 39 weeks the new EDD?

Study Design and Setting This Systematic Review was conducted at a tertiary centre, between July and September 2025. Study had been reviewed by the appropriate ethics committee (Certificate number 2025/07/OG/02 dt 01 Jul 2025) and had been performed in accordance with the ethical standards described in an appropriate version of the 1975 Declaration of Helsinki, as revised in 2000. The review has also been registered in PROSPERO International prospective register of systematic reviews with CRD420251136664. Search Strategy and Data Sources A systematic literature search was conducted to identify studies evaluating the impact of elective induction of labor (IOL) in low-risk pregnancies beyond 39 weeks of gestation. The search was performed across the following electronic databases: PubMed, MEDLINE, Cochrane Library, and Google Scholar, covering publications from inception to May 2025. Only articles published in English were considered. The reference lists of relevant studies, clinical guidelines, and major trial publications were also manually screened for additional eligible studies. The following search terms were used in various combinations with Boolean operators (AND, OR): “elective induction of labor,” “39 weeks induction,” “low-risk pregnancy,” “expectant management,” “cesarean section,” “ARRIVE trial,” and “maternal and neonatal outcomes.” Eligibility Criteria Studies were eligible for inclusion if they met all of the following criteria: • Reported on elective induction of labor at or beyond 39 weeks of gestation • Included only low-risk pregnancies (defined as singleton, cephalic presentation, absence of major maternal comorbidities) • Included a comparison group managed expectantly beyond 39 weeks • Reported at least one maternal (e.g., cesarean delivery, hypertensive disorders) or neonatal outcome (e.g., NICU admission, Apgar scores) • Study design was a randomized controlled trial, systematic review, or prospective/retrospective cohort study The following were excluded: • Studies including high-risk pregnancies, multiple gestations, or fetal anomalies • Studies focused solely on induction techniques or protocols without outcome data • Editorials, commentaries, or expert opinions lacking original data Study Selection All identified articles were screened in two stages. First, titles and abstracts were reviewed to exclude clearly irrelevant studies. Full texts of potentially eligible studies were then assessed against the inclusion and exclusion criteria. Thirteen studies were ultimately included in this review: two randomized controlled trials, one systematic review and one meta-analysis, one epidemiologic analysis of trial data, and eight cohort studies from various high-resource settings. Data Extraction Data were independently extracted from each included study using a standardized form. Extracted variables included: • Study design and geographic setting • Sample size and population characteristics • Gestational age at induction • Comparator group details (expectant management or spontaneous labor) • Maternal outcomes: cesarean delivery, hypertensive disorders, postpartum complications • Neonatal outcomes: NICU admission, Apgar scores, respiratory distress, composite morbidity Discrepancies in data extraction were resolved through discussion among the review authors. Data Synthesis Due to heterogeneity in study designs, populations, and outcome reporting, a quantitative meta-analysis was not performed. Instead, a narrative synthesis was conducted to summarize key findings across studies. Emphasis was placed on comparing elective induction with expectant management (rather than spontaneous labor) to reflect real-world clinical decision-making. Results were stratified by maternal and neonatal outcomes and discussed in the context of evolving clinical guidelines and implementation considerations.

This review includes 13 studies examining the outcomes of elective induction of labor (IOL) in low-risk pregnancies beyond 39 weeks, encompassing randomized controlled trials (RCTs), systematic reviews, and large observational cohorts. The results are organized thematically by maternal and neonatal outcomes and comparative study design. 1. Maternal Outcomes Caesarean Delivery Rates (Figure 1) • Grobman et al., (2019) [7]: Elective IOL at 39 weeks resulted in a significantly lower caesarean rate compared to expectant management (26.4% vs 29.1%; Relative Risk, 0.83; CI: 0.74-0.93). • Caughey et al. (2009) [5]: Meta-analysis of 9 RCTs showed a pooled Odds Ratio (OR) of 1.22 (95% CI: 1.07–1.39) in favor of induction, indicating higher caesarean rates in expectant management. • Darney et al. (2013) [4] and Cheng et al. (2012) [3]: Retrospective cohort studies demonstrated lower caesarean risk among women undergoing elective induction at 39 weeks compared to those expectantly managed beyond 39 weeks. • Vahratian et al. (2005) [8] and Glantz (2005) [9]: Studies comparing IOL to spontaneous labor (rather than expectant management) reported increased caesarean rates, though the comparator group was non-equivalent and potentially biased. • Kawakita et al. (2017) [10] found no increase in caesarean risk with non-medically indicated induction among morbidly obese women, and even a reduction in caesarean at full term in multiparas (5.4% vs 7.9%). • Harper et al. (2012) [11] highlighted longer latent phases in induced labors but comparable active phase progress, cautioning against premature arrest diagnoses before 6 cm. • ACOG/SMFM (2014) [12] consensus emphasized redefining labor dystocia and endorsed avoiding caesareans for slow but progressive labor before 6 cm dilation Figure 1. Caesarean delivery rates in elective IOL vs expectant management. Hypertensive Disorders of Pregnancy • ARRIVE Trial [2]: Incidence of hypertensive disorders was lower in the induction group (9.1%) versus expectant management (14.1%). • Observational data indicated variable findings, with some showing no significant differences, potentially due to differing gestational age ranges and definitions. Other Maternal Morbidity • Harper et al. and ACOG both underscored that active labor begins after 6 cm, and that applying traditional thresholds may over-diagnose arrest disorders in induced labors. • Length of stay: ARRIVE reported a slightly longer labor and delivery stay but shorter postpartum hospital stay in the IOL group. • Postpartum complications such as hemorrhage or infection were not significantly different across most studies. 2. Neonatal Outcomes (Figure 2) • ARRIVE Trial [2]: Primary composite neonatal outcome (e.g., perinatal death, respiratory support) occurred in 4.3% of neonates in the IOL group versus 5.4% in the expectant group (not statistically significant, P = 0.049). • Darney et al. [4]: Elective IOL at 39 weeks was associated with lower NICU admission rates and improved respiratory outcomes compared to those delivered later. • Systematic Review (Caughey et al.) [5]: Found a reduced risk of meconium-stained amniotic fluid with induction (OR 2.04; 95% CI: 1.34–3.09 in favor of IOL). • Walker et al. (INDEX trial) [13]: Though focused on IOL at 41+0 weeks, showed lower perinatal mortality with IOL versus expectant management, indirectly supporting the safety of timed delivery approaches. Figure 2. Neonatal outcomes with induction of labour (IOL) versus expectant management. Table 1. Summary of Key Results Study Design Population Gestational Age Comparator Key Outcomes Main Conclusion Carmichael & Snowden (2019) Epidemiologic critique Interpretation of ARRIVE data — — Focus on validity, selection bias, generalizability ARRIVE valid internally, external validity limited to high-resource settings ARRIVE Trial (Grobman et al., 2018) RCT, Multicenter 6106 low-risk nulliparas 39+0 to 39+4 Expectant management (until 42+2) ↓ Caesarean (18.6% vs 22.2%), ↓ hypertensive disorders, similar neonatal composite Elective IOL at 39 weeks is safe and lowers C-section risk Kawakita et al. (2017) Retrospective cohort 6,833 morbidly obese women ≥39+0 Expectant management ↓ Caesarean in multiparas, ↓ macrosomia, ↓ NICU Non-medically indicated induction is safe in obese women Walker et al. (INDEX Trial, 2016) RCT 619 nulliparas ≥41+0 Induction vs Expectant mgmt ↓ Perinatal mortality in IOL group; Similar caesarean rate; ↓ stillbirth Supports induction at 39 wks in older women ACOG / SMFM (2014) Consensus guidelinemeta N/A (policy-level) N/A Historic labor standards Redefines active labor at 6 cm; discourages early caesareans Caesarean for arrest should not be diagnosed <6 cm; longer latent phase acceptable Darney et al. (2013) California database study 362,000+ low-risk nulliparas 39, 40, 41 weeks Expectant mgmt ↓ Maternal and neonatal morbidity at 39 weeks induction Elective IOL at 39 weeks safest Cheng et al. (2012) Retrospective cohort 442,000+ births 39–41 weeks Expectant mgmt ↓ C-section, ↓ neonatal morbidity with elective IOL Supports elective IOL over expectant mgmt Harper et al. (2012) Retrospective cohort 5,388 term women ≥37+0 Spontaneous labor Longer latent labor in IOL; active phase similar Arrest diagnoses before 6 cm should be avoided in induced labors Stock et al. (2012) National retrospective cohort 1.2 million+ singleton births 37–41 weeks Spontaneous labor ↑ C-section and NICU with IOL vs spontaneous Results confounded by comparator choice Caughey et al. (2009) Systematic Review (36 studies) RCTs & Obs studies Mostly ≥41 weeks Expectant vs Elective IOL OR for C-section = 1.22 for expectant; ↑ meconium-stained fluid Elective IOL reduces caesarean and some neonatal risks ≥41 weeks Glantz (2005) Observational ~7000 term pregnancies ≥39 weeks Expectant mgmt ↑ C-section and NICU in IOL Elective IOL may increase interventions Vahratian et al. (2005) Observational Nulliparous elective IOL 37–42 weeks Spontaneous labor ↑ C-section in induced group May reflect non-equivalent comparator Vrouenraets et al. (2005) Prospective cohort 700 nulliparas Term Elective IOL vs spontaneous Higher C-section with lower Bishop Bishop score critical in predicting outcome

The management of low-risk pregnancies at term continues to evolve, particularly in light of growing evidence supporting elective induction of labor (IOL) at 39 weeks. This review synthesizes data from randomized trials, systematic reviews, and large observational studies, collectively indicating that elective IOL at 39 weeks may offer measurable maternal and neonatal benefits without increasing the risk of adverse outcomes. Elective Induction and Caesarean Risk One of the most consistent and clinically significant findings across studies is the reduction in caesarean delivery rates associated with elective IOL at 39 weeks. The ARRIVE trial [2], the most rigorous randomized controlled trial on this topic, demonstrated a 16% relative reduction in caesarean birth compared to expectant management. These findings were echoed by large retrospective cohort studies by Cheng et al. [3] and Darney et al. [4], both of which demonstrated significantly lower caesarean delivery rates among women electively induced at 39 weeks versus those expectantly managed. A systematic review by Caughey et al. [5] supported this association, reporting an odds ratio (OR) of 1.22 (95% CI: 1.07–1.39) for caesarean delivery in expectantly managed pregnancies compared to elective induction. In contrast, earlier observational studies such as those by Glantz, Vahratian et al, and Vrouenraets et al reported increased caesarean rates with induction; however, these studies used spontaneous labor as a comparator—an approach that introduces selection bias, as it excludes the real alternative faced in clinical decision-making: expectant management [9] [8] [14]. When appropriately compared to expectant management, elective induction at 39 weeks appears to reduce the likelihood of caesarean delivery, particularly in nulliparous women. Maternal Morbidity Beyond caesarean delivery, elective IOL at 39 weeks may also reduce the incidence of hypertensive disorders of pregnancy, a finding observed in both the ARRIVE trial [2] and real-world datasets like those from Darney et al. [4]. Given the significant risks associated with hypertensive disorders—including maternal end-organ dysfunction and fetal compromise—reducing the time at risk for their development is clinically meaningful. Other maternal outcomes such as postpartum hemorrhage, infection, and operative delivery rates were generally not significantly different across study arms. The ARRIVE trial also reported a trade-off of a slightly longer stay in labor and delivery with induction, counterbalanced by a shorter postpartum hospital stay [2]. Neonatal Outcomes Neonatal outcomes were either comparable or improved in the elective induction group across several studies. The ARRIVE trial found a trend toward reduced composite neonatal morbidity—particularly fewer cases requiring respiratory support—though the difference narrowly missed statistical significance (P=0.049) [2]. Studies by Darney et al. [4] and Cheng et al. [3] observed significantly lower NICU admissions and improved neonatal respiratory outcomes among neonates delivered via elective IOL at 39 weeks. Additionally, Caughey et al. [5] noted a significantly reduced incidence of meconium-stained amniotic fluid in the induction group (OR 2.04; 95% CI: 1.34–3.09), suggesting that planned delivery before late-term complications manifest may reduce fetal exposure to stress. Conversely, studies such as those by Glantz and Stock et al. , which compared induction to spontaneous labor, reported higher NICU admission rates and adverse neonatal events in the induction group [9] [15]. These findings must be interpreted cautiously due to differences in comparator group selection and lack of adjustment for confounding variables. Importantly, the INDEX trial by Walker et al. —though focused on induction at 41+0 weeks—demonstrated a reduction in perinatal mortality in the induction arm, indirectly supporting the concept that timely induction can prevent late-term complications when expectant management continues [13]. Validity and generalizability While the internal validity of the ARRIVE trial is robust due to its randomized design and large sample size, external validity remains a limitation. The study was conducted in high-resource academic hospitals with standardized induction protocols, where baseline caesarean rates were lower than national averages. As highlighted by Carmichael and Snowden , the generalizability of ARRIVE's findings to community or low-resource settings depends on the local ability to implement structured labor management guidelines [2]. However, supporting real-world evidence from Cheng, Darney, and others provides confidence that beneficial outcomes can be replicated, even in non-trial settings, provided adequate institutional capacity and provider training exist [3] [4]. Clinical Implications and Patient-Centered Care The accumulating evidence supports a shift in perspective: elective induction at 39 weeks in low-risk nulliparous women is not only safe but may be preferable to expectant management. However, implementation should be accompanied by shared decision-making. While many patients may welcome the predictability and reduced risk of complications, others may prefer spontaneous onset for personal, cultural, or physiologic reasons. A balanced, informed approach to delivery planning is essential [16] [17]. Limitations of the Evidence Base Despite the strength of data from trials and observational cohorts, gaps remain. Some observational studies suffered from residual confounding and suboptimal comparators. Few studies have assessed long-term maternal and neonatal outcomes, and cost-effectiveness analyses are still limited. There is also a need for more evidence among multiparous women, underrepresented populations, and in resource-limited settings. The evolving evidence presented in this review offers important food for thought and underscores the need for further evaluation through real-world implementation studies. A unified clinical approach will ultimately require consensus development by professional bodies and institutional committees to ensure safe, equitable, and evidence-based adoption of elective induction at 39 weeks

The collective findings from high-quality randomized and observational studies support elective induction of labor at 39 weeks as a safe and potentially advantageous option in low-risk pregnancies. It reduces caesarean rates, lowers the risk of hypertensive complications, and does not adversely affect neonatal outcomes. With appropriate institutional readiness and shared decision-making, 39 weeks may indeed represent a new evidence-based standard for delivery timing. This review concludes that for many low-risk pregnancies, “39 weeks is the new EDD.”

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