News Release

Labor induction at 40 weeks associated with lower risk of perinatal mortality

Peer-Reviewed Publication


Induction of labor at 40 weeks in nulliparous women aged 35 and older is associated with reduced risk of in-hospital perinatal death, according to an analysis of English Hospital Episode Statistics published this week in PLOS Medicine. The observational study, conducted by Hannah E. Knight of the London School of Hygiene & Tropical Medicine, and colleagues, provides further evidence that induction at or near the due date may be safer than expectant management in this group.

Guidelines recommend induction of labor between 41 and 42 weeks of gestation to prevent the risks associated with prolonged pregnancy. Women having their first baby at age 35 years or over are at increased risk of pregnancy complications, including perinatal death. To better understand the risks and benefits of elective induction in this group, Knight and colleagues analyzed a national dataset of 77,327 such mothers giving birth between 2009 and 2014. They found that induction of labor at 40 weeks (compared with expectant management) was associated with a lower risk of in-hospital perinatal death (0.08% versus 0.26%; adjusted risk ratio [adjRR] 0.33; 95% confidence interval [CI] 0.13-0.80, P = 0.015) and meconium aspiration syndrome (0.44% versus 0.86%; adjRR 0.52; 95% CI 0.35-0.78, P = 0.002). Induction at 40 weeks was also associated with a slightly increased adjusted risk of instrumental vaginal delivery (adjRR 1.06; 95% CI 1.01-1.11, P = 0.020) and emergency caesarean section (adjRR 1.05; 95% CI 1.01-1.09, P = 0.019). The number needed to treat (NNT) analysis indicated that 562 (95% CI 366-1,210) inductions of labor at 40 weeks would be required to prevent 1 perinatal death.

Unmeasured confounding may have influenced these results, and inductions and/or outcomes may have been under-recorded in the database. However, this association provides evidence that, as the authors state, "[b]ringing forward the routine offer of induction of labour from the current recommendation of 41-42 weeks to 40 weeks of gestation in this group of women may reduce overall rates of perinatal death."



The authors received no specific funding for this work.

Competing Interests:

We have read the journal's policy and the authors of this manuscript have the following competing interests: GCS is a member of the Editorial Board of PLOS Medicine. GCS receives/has received research support from GE (supply of 2 diagnostic ultrasound systems), from Roche (supply of equipment and reagents for biomarker studies, value £596,142), and from GSK (£199,413 for in vitro studies on human myometrium). GCS has been paid to attend advisory boards by GSK (preterm birth) and Roche (preeclampsia biomarkers). GCS has acted as a paid consultant to GSK (preterm birth). GCS has received support to attend a scientific meeting from Chiesi. GCS is a named inventor in a patent submitted by GSK for a novel application of an existing GSK compound for the prevention of preterm birth (PCT/EP2014/062602). GCS is a member of a GSK Data Safety Monitoring Committee for a trial of RSV vaccination in pregnancy and infancy.


Knight HE, Cromwell DA, Gurol-Urganci I, Harron K, van der Meulen JH, Smith GCS (2017) Perinatal mortality associated with induction of labour versus expectant management in nulliparous women aged 35 years or over: An English national cohort study. PLoS Med 14(11): e1002425.

Author Affiliations:

Department of Health Services Research and Policy, London School of Hygiene & Tropical Medicine, London, United Kingdom Royal College of Obstetricians and Gynaecologists, London, United Kingdom Department of Obstetrics and Gynaecology, University of Cambridge, NIHR Cambridge Comprehensive Biomedical Research Centre, Cambridge, United Kingdom


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