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Journal Summary: The ARRIVE trial: Labor induction vs expectant management in low-risk nulliparous women

Induction of labour at 39 weeks in low risk nulliparous women is associated with a reduction in caesarean section and a strong trend toward improved perinatal outcome.

Grobman WA et al for the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women. New Eng J Med 2018; 379:513-523.

Summary

Induction of labour (IOL) for nulliparous women at 39 weeks - when compared to expectant management- has been found to benefit some high risk groups, such as those over 35 years of age. Despite this, a policy of liberal induction has generally been thought to be associated with increased risks of caesarean section and adverse maternal outcomes. This trial sought to determine the impact of elective IOL at 39 weeks on perinatal outcomes and the rate of caesarean birth among low risk women.

This large, well-designed and well-executed trial included low risk women with no reason not be induced (eg planned caesarean section), and no reason not to be managed expectantly (eg hypertension, growth restriction, ruptured membranes etc). They successfully randomized over 3000 women to elective induction of labour (between 39 weeks and 39 weeks and 4 days) and a similar number to expectant management (who would forego elective delivery before 40 weeks 5 days and be delivered no later than 42 weeks 2 days). While labour management was at the discretion of the treating team, broad guidelines were provided. Cervical priming was encouraged, and it was suggested that sufficient time be allowed (up to 12 hours) in the latent phase of labour (up to 6cm) before making a diagnosis of arrested progress.  

The primary outcome was a composite of perinatal death or major morbidity, and the trial was powered for a 40% reduction in this outcome from an estimated risk of 3.5%. to 2.1%. The rate of caesarean delivery was a prespecified principal outcome. 

The trial revealed a non-significant trend toward improved perinatal outcome in those managed with induction (occurring in 4.3% of those induced compared with 5.4% in those managed expectantly, p=0.049), and a significant reduction in caesarean section among those induced (18.6% compared to 22.2% in those managed expectantly; relative risk, 0.84; 95% CI, 0.76 to 0.93.; number needed to treat 28).  These findings were unaltered when analysis was confined to those with an unfavourable cervix at the time of randomisation (Bishop score <5). There was also reduced hypertension in pregnancy in the induced group (9% versus 14%) and women randomised to induction also reported having less pain and feeling more in control in labour.  Women in the induction group spent longer in the labour unit, but had a reduced length of stay overall. 

Clinical implications

These findings provide valuable information to inform shared decision-making surrounding induction of labour at term in women without a medical indication. It is not a mandate for ‘induction for all at 39 weeks’ but it should reassure women undergoing induction- whether on medical advice or at maternal request- that the risk of caesarean section is lower, and that maternal and perinatal outcomes are similar, or better, when compared to expectant management.  Nevertheless, given the likely longer duration of high-resource ‘labour ward hours’, it is important to ensure that a request for non-medically indicated induction can be managed by both the health service and maternity care provider. Without the appropriate resources in place, the benefits seen in this trial may not be realized, and it may inadvertently put other laboring women at increased risk of adverse outcome. 

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