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HomeObstetricsLabour induction at 40 weeks reduces risk of perinatal death

Labour induction at 40 weeks reduces risk of perinatal death

Induction of labour 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. 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 labour 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 analysed a national dataset of 77,327 such mothers giving birth between 2009 and 2014. They found that induction of labour 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 labour 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."

Abstract
Background: A recent randomised controlled trial (RCT) demonstrated that induction of labour at 39 weeks of gestational age has no short-term adverse effect on the mother or infant among nulliparous women aged ≥35 years. However, the trial was underpowered to address the effect of routine induction of labour on the risk of perinatal death. We aimed to determine the association between induction of labour at ≥39 weeks and the risk of perinatal mortality among nulliparous women aged ≥35 years.
Methods and findings: We used English Hospital Episode Statistics (HES) data collected between April 2009 and March 2014 to compare perinatal mortality between induction of labour at 39, 40, and 41 weeks of gestation and expectant management (continuation of pregnancy to either spontaneous labour, induction of labour, or caesarean section at a later gestation). Analysis was by multivariable Poisson regression with adjustment for maternal characteristics and pregnancy-related conditions. Among the cohort of 77,327 nulliparous women aged 35 to 50 years delivering a singleton infant, 33.1% had labour induced: these women tended to be older and more likely to have medical complications of pregnancy, and the infants were more likely to be small for gestational age.
Induction of labour 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% 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 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 labour at 40 weeks would be required to prevent 1 perinatal death. Limitations of the study include the reliance on observational data in which gestational age is recorded in weeks rather than days. There is also the potential for unmeasured confounders and under-recording of induction of labour or perinatal death in the dataset.
Conclusions: Bringing forward the routine offer of induction of labour from the current recommendation of 41–42 weeks to 40 weeks of gestation in nulliparous women aged ≥35 years may reduce overall rates of perinatal death.

Authors
Hannah E Knight, David A Cromwell, Ipek Gurol-Urganci, Katie Harron, Jan H van der Meulen, Gordon CS Smith

[link url="https://www.sciencedaily.com/releases/2017/11/171114142337.htm"]PLOS material[/link]
[link url="http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1002425"]PLOS Medicine abstract[/link]

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