Fetal Macrosomia (LGA or Large for Gestational Age or “Large")
This article may refer to LGA babies simply as “large” for ease of readability. These definitions are terms used to describe a baby with an unusually high birth weight, regardless of gestational age (ACOG, 2020).

Retrospective Cohort/Observational Study
Comparing medical records of groups that differ in a characteristic or exposure to assess an outcome (NCI, N.D.).

Shoulder Dystocia
A birth complication in which a baby’s shoulder becomes stuck after the head is born, requiring additional maneuvers to deliver the body after gentle traction has failed (RCOG, 2026).

Brachial Plexus Injury
Damage to the network of nerves connecting the spinal cord to the shoulder, arm, and hand. It can occur during birth and cause weakness, loss of sensation, or paralysis in the affected arm (NINDS, 2026. Occurrence is shown to be impacted by provider training (CROFTS ET AL., 2016).

Hypoxic-ischemic Encephalopathy
Brain injury caused by insufficient oxygen and blood flow to the brain. In newborns, it can occur before, during, or shortly after birth and range from mild to severe (CLEVELAND CLINIC, 2023).

Late pregnancy ultrasound can estimate fetal weight, but it cannot determine a baby's actual birth weight. Even when performed correctly, ultrasound estimates become less accurate as pregnancy advances, particularly at the very end. Because of this uncertainty, some babies suspected to be "too large" are ultimately born at an average weight, while some truly large babies are underestimated. This is reflected in the trials & studies below (LOPIAN ET AL., 2026; GARDOSI ET AL., 2025).

"The diagnosis of fetal macrosomia is imprecise. For suspected fetal macrosomia, the accuracy of estimated fetal weight using ultrasound biometry is no better than that obtained with abdominal palpation." (ACOG, 2020)

“A Review of Late Pregnancy Ultrasounds in Low-Risk Pregnancies”

This study evaluates big baby diagnosis accuracy & the subsequent interventions

Details: This retrospective cohort study examined 21,743 singleton births following routine ultrasound at 35–37 weeks. Some babies received a suspected large baby diagnosis and others did not. This study followed these babies through delivery to determine ultrasound accuracy of suspected big babies as well as to observe the potential impact on delivery interventions.

Short Takeaway: Among babies actually born large for gestational age, those identified large before birth underwent more inductions and cesareans without a demonstrated improvement in neonatal outcomes compared with babies born large with no diagnosis.

The 2.1 ounce different is not considered a significant enough weight difference to significantly impact delivery results, therefore authors infer prenatally labelling did impact deliveries, however this is observational & not trial backed certainty.

Authors Note: In this study, normal sized babies with a big baby diagnosis had more intrapartum cesareans than babies who were actually large but prenatally undetected.

Authors contextual bias note: The study did not report how the shoulder dystocia’s were defined, therefore this leaves room for subjective results & not accurate statical conclusions.

(LOPIAN ET AL., 2026)

This trail compares induction vs no induction in diagnosed big babies. Primary objective was to observe shoulder dystocia differences.

Details: This open-label randomized controlled trial assigned 2,893 women with an ultrasound-suspected large for gestational age baby to induction at 38+0–38+4 weeks or standard care (induction only with indication).

Additional Trial Note: The trial ended before reaching its planned enrollment because shoulder dystocia occurred less frequently than anticipated and many standard-care participants delivered earlier than expected.

*A Note on the Secondary Analysis Shoulder Dystocia Findings: The primary analysis found that induction did not significantly reduce shoulder dystocia (2.3% induction vs 3.1% no induction). Researchers suggested that this result may have been diluted because many standard-care participants delivered earlier than anticipated, narrowing the intended timing difference between groups. A secondary analysis of trial data looked specifically at participants who followed the intended timing gap (were not induced before 38+4) and did find slightly fewer cases of shoulder dystocia with induction (2.3% induction vs 3.7% without induction). However, there was no improvement in birth injury or other neonatal outcomes between these groups (GARDOSI ET AL., 2025).

Shoulder dystocia diagnosis in this trial was not clarified. We do know the primary criteria were failure of gentle traction and the need for additional maneuvers, however we do not know how long providers allowed and if they allowed a fresh contraction before stepping in and administering maneuvers. We also know that the diagnosis of a big baby itself, as seen in Lopain et al, may increase diagnosis of shoulder dystocia.

Studies show us that it’s common for a normal sized baby to need a fresh contraction (LOCATELLI ET AL., 2011)

Author: These findings would even more so apply to a larger baby.

In a prospective study of 789 term births, attendants waited for the next contraction. The average head-to-body interval was 88 seconds, without a clinically meaningful increase in neonatal acidemia (LOCATELLI ET AL., 2011). This study was not exclusively for larger babies but can draw a safe average for a normal sized baby of 88 seconds.

This article is provided for general educational and informational purposes only and does not constitute individualized medical advice, diagnosis, or treatment. Research findings and professional guidelines may not apply to every person or clinical circumstance. Discuss decisions about your care with a qualified healthcare professional who understands your individual history and needs. Although The Birth Review makes reasonable efforts to represent sources accurately, information may become outdated, studies may contain limitations, and qualified experts may interpret the same evidence differently.

(ACOG, 2020) American College of Obstetricians and Gynecologists. (2020). Practice Bulletin No. 216: Macrosomia. Obstetrics & Gynecology, 135(1), e18–e35. https://doi.org/10.1097/AOG.0000000000003606

(CLEVELAND CLINIC, 2023) Cleveland Clinic. (2023). Hypoxic-ischemic encephalopathy (HIE). https://my.clevelandclinic.org/health/diseases/hypoxic-ischemic-encephalopathy-hie

(GARDOSI ET AL., 2025) Gardosi, J., Ewington, L. J., Booth, K., et al. (2025). 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. The Lancet, 405(10491), 1743–1756. https://doi.org/10.1016/S0140-6736(25)00162-X

(LOCATELLI ET AL., 2011) Locatelli, A., Incerti, M., Ghidini, A., Longoni, A., Casarico, G., Ferrini, S., & Strobelt, N. (2011). Head-to-body delivery interval using “two-step” approach in vaginal deliveries: Effect on umbilical artery pH. The Journal of Maternal-Fetal & Neonatal Medicine, 24(6), 799–803. https://doi.org/10.3109/14767058.2010.531307

(LOPIAN ET AL., 2026) Lopian, M., Ulusoy, C. O., Mohamed, D., Segal, E., & Khalil, A. (2026). Screening for large-for-gestational-age neonates at term: Evidence of a labeling effect and increased intervention without neonatal benefit. American Journal of Obstetrics and Gynecology, 235(3), 686–698. https://doi.org/10.1016/j.ajog.2026.04.015

(NCI, N.D.) National Cancer Institute. (n.d.). Retrospective cohort study. NCI Dictionary of Cancer Terms. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/retrospective-cohort-study

(NINDS, 2026) National Institute of Neurological Disorders and Stroke. (2026). Brachial plexus injury. National Institutes of Health. https://www.ninds.nih.gov/health-information/disorders/brachial-plexus-injury

(RCOG, 2026) Royal College of Obstetricians and Gynaecologists. (2026). Shoulder dystocia: Green-top Guideline No. 42 (3rd ed.). https://doi.org/10.1111/1471-0528.70258

(CROFTS ET AL., 2016) Crofts, J. F., Lenguerrand, E., Bentham, G. L., et al. (2016). Prevention of brachial plexus injury—12 years of shoulder dystocia training: An interrupted time-series study. BJOG: An International Journal of Obstetrics & Gynaecology, 123(1), 111–118. https://doi.org/10.1111/1471-0528.13302