Fetal Macrosomia
A term describing a baby with a birth weight above a fixed cutoff, commonly 4,000 grams (approximately 8 lb 13 oz) or 4,500 grams (approximately 9 lb 15 oz), regardless of gestational age. There is no single universally accepted weight cutoff (ACOG, 2020).

Large for Gestational Age (LGA or “Large")
This article may refer to LGA babies simply as “large” for ease of readability. LGA is a term describing a baby whose weight is at or above the 90th percentile for gestational age—meaning the baby weighs more than approximately 90% of babies at the same stage of pregnancy (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).

Induction of Labor
The use of medication or medical procedures to start labor before it begins on its own (NHS, 2023).

Spontaneous Labor
Labor that begins on its own, without medication or medical procedures being used to start it. Pain relief or medication given after labor begins does not change how it started (NICE, 2023).

Maternal Hemorrhage (postpartum hemorrhage):
Excessive bleeding associated with childbirth. ACOG defines it as total blood loss of at least 1,000 mL (1 liter), or bleeding accompanied by signs or symptoms of low circulating blood volume, within 24 hours after birth, regardless of whether the birth is vaginal or cesarean (ACOG, 2017). Blood loss amounts qualifying hemorrhage vary per guidelines & studies.

The idea of a big baby can incite a lot of fear. We tend to hear absolute claims in both directions. “There is no risk to a big baby” or “you’re likely to have a shoulder dystocia if you don’t induce now” or maybe “the best thing to prevent a cesarean or tearing is inducing at 39 weeks”.

What does the evidence say about these claims? Well, it depends. It depends on which evidence, which methods are compared, and more. In this spotlight article we dive deep into an array of evidence on big babies, ultrasound & detection risk. We also explore induction risk and benefits supported by evidence. This array of research allows you to extract from this a risk benefit analysis that best fits your scenario and desires for your labor and birth. Set aside fear and look at the research. Here, we provide you the research, the context and the bigger picture of big babies.

Late pregnancy ultrasound can estimate fetal weight, but it cannot determine a baby's actual birth weight. Estimates of fetal weight are imperfect, and difficulty obtaining accurate measurements late in pregnancy can contribute to estimation errors (MILNER & AREZINA, 2018). 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 where we see missed or falsely detected big babies in 31.1% to 65.1% of studied populations (LOPIAN ET AL., 2026; GARDOSI ET AL., 2025).

“For suspected 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. This study used the same threshold as ACOG to define an LGA baby, at or above the 90th percentile (LOPIAN ET AL., 2026).

Study Limitations: This study did not exclude or separate out mothers with gestational diabetes, which is known to cause an elevated fetal weight and larger shoulder circumferences (LOPIAN ET AL., 2026; ACOG, 2020). This study also does not distinguish between mothers who received an epidural which is a known risk factors for shoulder dystocia (LOPIAN ET AL., 2026; CLEVELAND CLINIC, 2022).

Short Takeaway: Among babies actually born large for gestational age, suspected babies were associated with having more inductions, earlier births, more planned cesareans, more intrapartum cesareans, and more shoulder dystocia’s. Despite the previously listed measures taken, large for gestational age babies who were suspected vs unsuspected also suffered worse newborn adverse outcomes. When looking specifically at intrapartum cesareans, we see that babies who were actually not large for gestational age but were suspected large, had a higher rate of intrapartum cesareans than actual large babies who went undetected (LOPIAN ET AL., 2026).

Authors inference note: It’s unlikely that a 2.1 ounce weight difference impacted delivery outcomes substantially. It is a plausible inference that prenatal labeling could have impacted care and interventions. This inference was also expressed by the Lopian authors.

Authors contextual & summary note: The study did not report how the shoulder dystocia’s were defined, therefore this leaves room for subjective results & not accurate statical conclusions. However, we do see that the increased inductions in the suspected group did not decrease rates of dystocia’s, its actually associated with more dystocia’s.

Maternal Adverse Outcomes Includes: postpartum hemorrhage, high dependency/intensive care admission, anal sphincter injury (severe tears), or cesarean during labor. Thus, this percentage does not represent injuries alone.

(LOPIAN ET AL., 2026)

Observational studies can identify patterns and associations but cannot establish cause and effect. Differences in outcomes may reflect other factors, even after statistical adjustment.

A separate U.S. observational study of 64,030 women attempting vaginal birth at term found that women with a documented ultrasound weight estimate had higher odds of cesarean than those without a documented estimate, even after accounting for actual birth weight and other measured factors (FROEHLICH ET AL., 2016).

Authors Note on Froehlich: We can infer that in this study there was an association between detection of weight & increased cesareans as was also see in Lopian.

Back to Relevant Terminology

This study compares outcomes of babies who were induced vs spontaneous among babies suspected to be large for gestational age.

This retrospective study used records from University Hospital Brugmann in Brussels, Belgium, from 2015–2022. It compared 329 induced mothers with 218 mothers whose labor started spontaneously—547 total. Participants were carrying one baby estimated by ultrasound to be at or above the 90th percentile at 35–39 weeks and were eligible for vaginal birth. Mothers with diabetes were included; inductions for reasons other than suspected macrosomia were excluded.

*Hemorrhage was defined as blood loss exceeding 500 mL after vaginal birth or 1,000 mL after cesarean birth.

The 5 minute Apgar was the only significantly different outcome reported for babies. If there were any fatal outcomes these were not reported.

When actual birth weights were evaluated for each group, they both had about a 50% margin of error in diagnosis meaning about half of them in each group did not have a baby large for gestational age. All other newborn outcomes did not have a statistical difference.

(BADR ET AL., 2024)

This study looks compares outcomes for induced labors vs. spontaneous labors for babies who were all confirmed over 8 lb 13 oz after birth.

This retrospective U.S. study used delivery records from 1989–1991. It compared 46 induced mothers with 140 mothers whose labor started spontaneously—186 total. Participants had nondiabetic pregnancies. Eligibility was base off after birth weight and not ultrasound estimation.

Study Authors concluded: “We conclude that spontaneous rather than induced labor is associated with a lower chance of cesarean delivery among those fetuses with birthweights 4000 g or more.”

Of accessible information, a fatal outcome was not reported.

(FRIESEN ET AL., 1995)

There is currently no evidence comparing spontaneous labors with induced labors that challenges the evidence here. However, there are other studies like Boulvain 2015, that like big baby trial below, compare induction with usual care which includes inductions. Both have similar findings as big baby; overall benefit with earlier induction.

Back to Relevant Terminology

This trial compares induction vs. only indicated inductions (or usual care) 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 or usual care). This trial specifically enrolled women with babies above the 90th percentile customized estimated weight percentile, confirmed by scan (GARDOSI ET AL., 2025).

Limitations: Shoulder dystocia was very narrowly defined. The usual care group was still primarily inductions (815/1076) which does not allow us to see the impact on shoulder dystocia’s & cesareans when the labor is spontaneous vs induced (GARDOSI ET AL., 2025). Epidural use with inductions is increased and epidural use is a risk factor for shoulder dystocia (KINGSTON AND RICHMOND NHS FOUNDATION TRUST, 2024; CLEVELAND CLINIC, 2022).

Short Takeaway: Since most of the mothers in the usual care group were induced, this trial better compares earlier inductions with mostly later inductions rather than inductions for big baby compared with spontaneous big baby delivery. The results found a slight increase in cesareans (opposed to all observational evidence) as well as a slight increase in shoulder dystocia’s in usual care (mostly later inductions). The trial also found a slight increase in 1st, 2nd, and 3rd degree perineal tears in the induced group (GARDOSI ET AL., 2025).

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 early induction did not significantly reduce shoulder dystocia (2.3% induction vs 3.1% usual care). 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 a larger benefit and slightly fewer cases of shoulder dystocia with early induction (2.3% induction vs 3.7% usual care (mostly later inductions, some spontaneous). However, there was no significant 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 Lopian et al) may increase diagnosis of shoulder dystocia, and every baby in this trial had been labeled large for gestational age.

Back to Relevant Terminology

There is currently no evidence that compares inducing at 39 weeks (or earlier) with mothers who go into labor spontaneously & do not receive an epidural or labor augmentation. And as we see here the evidence on induced vs. just spontaneous is slim and not a large enough sample to be considered high grade evidence (FRIESEN ET AL., 1995; BADR ET AL., 2024). However, the promising contrast in outcomes should signal the need for further research in this area.

But since we do know that use of Pitocin for induction or augmentation is associated with increased epidural use (CLEVELAND CLINIC, 2022) and epidural use is an associated risk factor for shoulder dystocia (KINGSTON AND RICHMOND NHS FOUNDATION TRUST, 2024), this comparison needs more research to create a better understanding of all the options for reducing shoulder dystocia and possibly minimizing other impacts.

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

(BADR ET AL., 2024) Badr, D. A., Carlin, A., Kadji, C., Kang, X., Cannie, M. M., & Jani, J. C. (2024). Timing of induction of labor in suspected macrosomia: Retrospective cohort study, systematic review and meta-analysis. Ultrasound in Obstetrics & Gynecology, 64(4), 443–452. https://doi.org/10.1002/uog.27643

(CLEVELAND CLINIC, 2022) Cleveland Clinic. (2022, January 23). Shoulder dystocia. https://my.clevelandclinic.org/health/diseases/22311-shoulder-dystocia

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

(FRIESEN ET AL., 1995) Friesen, C. D., Miller, A. M., & Rayburn, W. F. (1995). Influence of spontaneous or induced labor on delivering the macrosomic fetus. American Journal of Perinatology, 12(1), 63–66. https://doi.org/10.1055/s-2007-994404

(FROEHLICH ET AL., 2016) Froehlich, R. J., Sandoval, G., Bailit, J. L., et al. (2016). Association of recorded estimated fetal weight and cesarean delivery in attempted vaginal delivery at term. Obstetrics & Gynecology, 128(3), 487–494. https://doi.org/10.1097/AOG.0000000000001571

(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

(KINGSTON AND RICHMOND NHS FOUNDATION TRUST, 2024) Kingston and Richmond NHS Foundation Trust. (2024, November 5). Induction of labour at 41 weeks and beyond: Making a decision. Patient leaflet directory—locate by title

(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

(NHS, 2023) National Health Service. (2023, November 1). Inducing labour. https://www.nhs.uk/pregnancy/labour-and-birth/inducing-labour/

(NICE, 2023) National Institute for Health and Care Excellence. (2023). Intrapartum care (NICE guideline NG235). https://www.nice.org.uk/guidance/ng235

(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