The 2025 Big Baby Trial

Currently, as of today’s date, neither the ACOG nor SMFM currently support routine early induction of labor for suspected fetal macrosomia, instead recommending individualized counseling and reserving elective cesarean for extreme estimated fetal weights. However, a 2025 multicenter, open-label, randomized controlled trial was published in the Lancet comparing induction of labor versus standard care in pregnant women with fetuses suspected to be large for gestational age. The study used a parallel-group design with 1:1 randomization, enrolling women from 106 NHS hospitals across England, Scotland, and Wales. The per-protocol analysis demonstrated a significant reduction (40%) in shoulder dystocia with induction of labor at 38- 38 weeks and 4 days. Is this in conflict with the ACOG current guidance? In this episode, we will review the “Big Baby study” from the Lancet and provide 3 main limitations of this very large study, review the importance of PP vs ITT results, and explain why more data is still needed. Listen in for details.

1. ACOG PB 178; 2017 (reaffirmed 2024)

2. 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.

3. Blaauwgeers, Anne N et al. Rethinking induction of labour for LGA fetuses: the Big Baby trial. The Lancet, Volume 406, Issue 10512, 1562