London School of Hygiene & Tropical Medicine

NHS data suggests inducing women with uncomplicated pregnancies at 39 weeks may reduce inequalities in adverse outcomes, according to a study by London School of Hygiene & Tropical Medicine researchers and partners. The research was carried out as part of the National Maternity and Perinatal Audit, evaluating maternity services across England, Scotland and Wales.

The findings, published in PLOS Medicine, indicate the greatest benefit of artificially starting labour at 39 weeks for reducing risks, compared with waiting for labour to begin naturally, is seen in women from more socioeconomically deprived areas and in women who are having their first baby.

But the authors highlight the need for more research to dig further into this evidence to guide clinical policy on induction and women’s choices at an individual level.

Adverse perinatal outcomes— which include stillbirths, neonatal deaths, preterm births, and other birth complications— are more common among women from deprived areas and ethnic minorities in England.

There is ongoing debate about whether to offer starting labour artificially at 39 weeks, rather than once overdue at 41-42 weeks, in low-risk pregnancies based on ethnicity or socioeconomic status.

In the new study, researchers analysed a database of all maternal hospital admissions in the NHS between January 2018 and March 2021. A total of 501,072 women with low-risk pregnancies who had not yet given birth at 39 weeks were included in the analysis. Of these, 47,352 (9.5%) were induced at 39 weeks.

The data showed that 3.3% (1,555 out of 47,352) of births in the induction group and 3.6% (16,525 out of 453,720) of births in the expectant management group – ie monitoring while waiting for labour to start naturally – had an adverse perinatal outcome.

After adjustment, researchers found a small benefit from induction of labour in low-risk pregnancies, with 360 inductions associated with avoiding one adverse outcome. However, the benefits of induction were mainly seen in women from more socioeconomically deprived areas and women having their first baby.

The authors acknowledge limitations of the study including the fact the routinely collected data used in the analysis did not include the reason for labour being induced, and some details of maternal risk factors such as body mass index and smoking were also not included in the data.

Senior co-author Dr Ipek Gurol-Urganci, Associate Professor of Health Services Research at LSHTM, said: "We used routinely collected administrative data from NHS hospitals in England. Our study highlighted that we urgently need detailed, accurate and complete information from each maternity unit, collected at national level, about why labour was induced, so that we get an even better understanding of the role that induction of labour can play in improving perinatal outcomes."

Senior co-author Professor Asma Khalil, Professor of Obstetrics and Maternal-Fetal Medicine at St George's University Hospitals NHS Foundation Trust, said: “Improved collection of data on the presence of risk factors is required to corroborate the role that induction of labour at 39 weeks in women with a low-risk pregnancy can play in reducing inequalities in risk of adverse perinatal outcomes.”

Publication 

P Muller, AM Karia, K Webster, F Carroll, G Dunn, A Fremeaux et al, Induction of labour at 39 weeks and adverse outcomes in low-risk pregnancies according to ethnicity, socioeconomic deprivation, and parity: A national cohort study in England. PLOS Medicine.  doi.org/10.1371/journal.pmed.1004259