Published in The Lancet, findings from The Big Baby Trial led by The University of Warwick, University Hospitals Coventry and Warwickshire NHS Trust (UHCW) 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.

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% 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.

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, 2893 women in 106 hospitals across Great Britain consented to be randomly allocated to induction of labour or standard care.

Eve Morgan, 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 for my baby.

“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 since, 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 Siobhan 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.”

Professor Jason 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 LancetLink opens in a new window

DOI: 10.1016/S0140-6736(25)00162-XLink opens in a new window

ENDS

For further information contact:

Matt Higgs, Media & Communications Officer (Science), The University of Warwick Matt.Higgs@Warwick.ac.uk / 07880 175403

Steven Box, Communications Officer, University Hospitals Coventry and Warwickshire NHS Trust, steven.box@uhcw.nhs.uk | Direct Line: 024 7696 5058 | Mobile: 07920 015224

Image Credit: Pexels - William Fortunato (Free to Use)

Notes to editors

The University of Warwick is one of the UK’s leading universities, marking its 60th anniversary in 2025. With over twenty-eight thousand students from 147 countries, it is currently ranked 9th in the UK by The Guardian University Guide. It has an acknowledged reputation for excellence in research and teaching, for innovation, and for links with business and industry. The recent Research Excellence Framework classed 92% of its research as ‘world leading’ or ‘internationally excellent’. The University of Warwick was awarded Midlands University of the Year by The Times and Sunday Times.

The Perinatal Institute is a multi-award winning national not-for-profit social enterprise based in Birmingham, working to enhance the safety and quality of maternity care. It is a qualified provider of maternity support services including education and training, standardised maternity records, fetal growth assessment and perinatal audit.

The National Institute for Health and Care Research's (NIHR) mission is to improve the health and wealth of the nation through research. They do this by:
• Funding high quality, timely research that benefits the NHS, public health, and social care;
• Investing in world-class expertise, facilities, and a skilled delivery workforce to translate discoveries into improved treatments and services;
• Partnering with patients, service users, carers, and communities, improving the relevance, quality, and impact of our research;
• Attracting, training, and supporting the best researchers to tackle complex health and social care challenges;
• Collaborating with other public funders, charities, and industry to help shape a cohesive and globally competitive research system;
• Funding applied global health research and training to meet the needs of the poorest people in low- and middle-income countries.
NIHR is funded by the Department of Health and Social Care. Its work in low- and middle-income countries is principally funded through UK Aid from the UK government.