Early Induction Reduces Shoulder Dystocia Without Increasing Adverse Events, Suggests Study

Published in The Lancet, the multicentre, open-label randomized controlled trial, known as the Big Baby trial, was led by Prof Jason Gardosi from Warwick Medical School, UK. It assessed whether early induction of labour could help prevent shoulder dystocia—an obstetric emergency where the baby's shoulders get stuck during delivery—in pregnancies suspected to involve large-for-gestational-age (LGA) fetuses.

The trial enrolled 2,893 women aged 18 or older with singleton pregnancies and ultrasound-estimated fetal weights above the 90th percentile for their gestational age between 35 and 38 weeks of gestation. Participants were recruited from 106 hospitals across England, Scotland, and Wales and were randomly allocated to either early induction (between 38+0 and 38+4 weeks) or standard care.

The primary outcome was the rate of shoulder dystocia, evaluated by an independent panel that was unaware of group assignments.

The study revealed the following findings:

• Early induction was expected to result in births approximately 10.5 days earlier than those in standard care.
• Babies in the early induction group were anticipated to have birthweights around 300 grams lower than those in the standard care group.
• In the intention-to-treat analysis, shoulder dystocia occurred in 2.3% of deliveries in the induction group compared to 3.1% in the standard care group, but this difference was not statistically significant (risk ratio 0.75).
• The per-protocol analysis showed a statistically significant reduction in shoulder dystocia in the induction group (2.3%) compared to the standard care group (3.7%), with a risk ratio of 0.62.
• The incidence of serious adverse events was comparable between the two groups.
• One neonatal death occurred in the induction group due to infection, and another in the standard care group due to shoulder dystocia-related asphyxia.
• Adverse maternal events were reported in 6.1% of the induction group and 7.5% of the standard care group, a difference that was not statistically significant.

Although the trial was stopped early due to a lower-than-expected rate of shoulder dystocia in the standard care group, the findings suggest that inducing labour slightly earlier in pregnancies with suspected LGA fetuses may help reduce the risk of shoulder dystocia, particularly when delivery occurs strictly between 38+0 and 38+4 weeks.

The study emphasizes that early induction does not need to happen before 38 weeks to confer this benefit, nor does it negatively impact neonatal outcomes such as the need for phototherapy. Furthermore, early induction may slightly extend hospital stay before delivery but could reduce the likelihood of operative deliveries.

The authors highlight the importance of shared decision-making with expectant mothers. Given that fetal weight estimation via ultrasound carries a degree of error, discussions should include the pros and cons of early delivery versus continued expectant care or elective caesarean section. Ultimately, the trial adds valuable insight to guide timing decisions in managing pregnancies where LGA is suspected.

Reference:

Gardosi J, Ewington LJ, Booth K, Bick D, Bouliotis G, Butler E, Deshpande S, Ellson H, Fisher J, Gornall A, Lall R, Mistry H, Naghdi S, Petrou S, Slowther AM, Wood S, Underwood M, Quenby S. Induction of labour versus standard care to prevent shoulder dystocia in fetuses suspected to be large for gestational age in the UK (the Big Baby trial): a multicentre, open-label, randomised controlled trial. Lancet. 2025 May 17;405(10491):1743-1756. doi: 10.1016/S0140-6736(25)00162-X. Epub 2025 May 1. PMID: 40319899.