Results from UHCW-led trial empowers women to choose how to deliver big babies

Published in The Lancet, findings from The Big Baby Trial led by University Hospitals Coventry and Warwickshire (UHCW) NHS Trust, The University of Warwick and the Perinatal Institute, provides crucial new information to help women choose how to safely deliver babies suspected to be large for their age.

At birth, large babies are at risk of shoulder dystocia, a complication where the baby becomes stuck as a shoulder is caught under the mother’s pelvic bone. Contrary to previous evidence, this trial, funded by the National Institute for Health and Care Research (NIHR) and sponsored by UHCW, showed that delivery by a week to 10 days earlier reduced this risk. It also reduced the need for emergency caesarean section and does not increase the risk of tearing for the mother.

Led by Professor of Obstetrics Siobhan Quenby MBE of the Directorate of Biomedical Sciences (Warwick Medical School), The University of Warwick and Honorary Consultant at UHCW and Professor Jason Gardosi MBE from the Perinatal Institute, Birmingham, the Big Baby Trial is the largest trial to date, including twice as many pregnancies as all previous studies taken together. Between June 2018 and October 2022, 2,893 women in 106 hospitals across Great Britain consented to be randomly allocated to induction of labour or standard care.

Professor Quenby said: ‘’I am delighted that this trial has provided data that empowers women to choose how and when they want to deliver their baby.”

Standard screening for big babies in the UK is an important part of antenatal care, alongside surveillance for small babies to check for restricted growth. Large babies are defined as those who weigh more than 90 per cent of other babies the same age, which increases their risk of complications including fractures, nerve damage or brain injury. However, this research found that these complications were rare and attributed this to an overall high level of training in managing deliveries of big babies.

Eve Morgan, a participant in the Big Baby Trial, said: “Everyone was surprised when I was diagnosed with diabetes during pregnancy. Because diabetes and big babies are linked, I thought it was a good idea to join the study and get extra monitoring throughout my pregnancy, although I wanted a natural birth.

“As I got closer to my due date, the monitoring predicted that Magnus would reach 9lbs at full term. I didn’t want to be induced with hormones, but I was happy to try the ‘stretch and sweep’ method as this can trigger labour and you can stick to your birth plan. The second attempt seemed to get the baby moving and I ended up giving birth to Magnus in a water bath!”   

The study provides evidence for clinical management options that increases choices for women with large babies, to choose a birth plan that can include: 

• Waiting for labour to start naturally without worrying about increasing risk to babies if delivery occurs on a labour ward with highly trained staff;
• Choosing a planned Caesarean section, or
• Induction at 38 weeks to reduce the risk of the baby’s shoulder being caught, without having to worry that this increases the risk of emergency Caesarean section or mother’s tearing during delivery.

Nadine Montgomery, whose birth was complicated with shoulder dystocia 25 years ago and resulted in her son requiring ongoing care, said: “I am ever so pleased that we now have, for the first time, pivotal evidence to allow women to make free and valid choices about how to give birth to bigger babies. This will undoubtedly lead to safer outcomes for mothers and babies. Incredible work - well done to everyone involved!”

Professor Gardosi added: “Thanks to the many women who agreed to participate in the trial, we have been able to research the evidence that will help women with big babies to make informed choices.”

Katie Morris, NIHR National Clinical Specialty Lead for Reproductive Health and Childbirth, explains: “Large babies can present complications at birth which injure both mother and baby. The findings of this world-leading trial offer crucial evidence that will help improve the chances of a safe birth and help expectant mums and medical staff make the most informed choices.”

The full paper is published in The Lancet.