Title: Induction of labour for predicted macrosomia (The 'Big Baby Trial')
Funder: Department of Health and Social Care

Abstract: Introduction: Large for gestational age babies have an increased risk of shoulder dystocia (a vaginal cephalic delivery that requires additional obstetric manoeuvres to deliver the fetus after the head has delivered and gentle traction has failed). Shoulder dystocia can result in birth injury for the baby and the women. Current guidelines from the Royal College of Obstetricians and Gynaecologists (RCOG) recommend no antenatal intervention if a large for gestational age baby is suspected, but a recent randomised controlled trial from France and subsequent Cochrane Review found that induction at 37-40 weeks reduced the incidence of shoulder dystocia and associated problems. Aim: We will investigate whether a policy of induction of labour at 38+ weeks gestation in women with babies considered large for gestational age (>90th customised centile of estimated fetal weight) will reduce the incidence of shoulder dystocia. Method: Multicentre prospective randomised controlled trial, with induction of labour at 38+ weeks or expectant management of fetuses found to be large for gestational age at ultrasound scan between 35 and 38 weeks. Recruitment will take place in NHS hospitals that use the RCOG recommended customised GROW charts for fetal growth assessment; these charts adjust for physiological maternal characteristics and thereby improve the prediction of abnormal outcomes. The trial will run over 42 months, including a two year recruitment period to enrol 4000 women identified as having large for gestational age pregnancies. Evaluation: The incidence of shoulder dystocia is the primary outcome, with assessment of the validity of the diagnosis, for all randomised women, by an independent expert group. Secondary outcomes will include birth injury, fractures, neonatal asphyxia, maternal haemorrhage, perineal trauma, caesarean section rate, and length of inpatient stay of mother and baby. To inform the interpretation of the findings and where outcomes make a clearly related set, composite outcomes for intra-partum birth injury, prematurity and maternal intra-partum complications will be reported. There will be a maternal and paternal experience survey and a thorough health economic assessment, comparing the cost of the intervention with savings through prevention of shoulder dystocia and other maternal or neonatal complications. We will also seek to collect information about pregnancy outcomes of eligible women who declined to be randomised. Outcome: This trial will help to answer an important question concerning the possibility of preventing serious adverse outcome of pregnancy and labour within the context of routine NHS maternity care. It will inform healthcare policy nationally and internationally and provide important information for maternal choice.

Lay abstract: Difficulty in delivering the shoulders, after a baby’s head has been delivered, can be a serious complication during a vaginal birth. In most cases where this happens, the baby is larger than average. It has been suggested that if we can predict, by ultrasound scan in the last weeks of pregnancy, which babies are particularly large and at the highest risk of shoulder dystocia, then we could deliver them a week or two earlier by inducing labour, which would reduce the chance of this complication. It is not clear whether it is better for women and their babies to have labour induced early or to wait for labour to begin naturally. To find out whether delivering large babies earlier is the right thing to do for the baby and mother, a clinical trial is needed. We propose to study 4,000 pregnant women whose ultrasound scans suggests that their babies are particularly large and may be at risk of difficulty with delivery of the shoulders during birth. With the women’s consent, she will be allocated at random into either an early induction of labour group, with the aim to give birth at, or soon after, 38 weeks, or a control group where care is as usual and the start of labour is awaited, unless it becomes necessary to induce labour after 38 weeks. We will compare outcomes between the two groups to look at whether, as a result of induction of labour at about 38 weeks, there were fewer complications such as difficulty with the delivery of the baby’s shoulders. We will also assess the benefits and risks to women and their babies in each group. This trial will help decide what the safest method is to care for pregnant women where, because of the large size of the baby, complications may occur during labour and birth.

Research activity codes: 7.3 MANAGEMENT AND DECISION MAKING
Health categories: REPRODUCTIVE HEALTH AND CHILDBIRTH