Official guidelines do not recommend or recommend against routine late pregnancy ultrasounds in low-risk pregnancies. Instead, they recommend reserving them for pregnancies with specific medical indications.

Routine ultrasound screening has not been shown to improve important maternal or perinatal outcomes compared with selective ultrasounds performed only for clinical indications in healthy, low-risk pregnancies.

Randomized trials have not consistently demonstrated an increase in induction or cesarean birth. However, trials and or observational studies do show that increased detection of suspected abnormalities or fetal concerns (like IUGR or big baby) is associated with increased inductions, cesareans and NICU admittance without demonstrating an improvement to neonatal outcomes.

A single ultrasound suggesting a baby is “small” or “large” should not be interpreted in isolation when decisions about induction of labor or cesarean birth are being considered.

Ultrasounds are a valuable tool (when indicated) in late pregnancy for seeking to evaluate things like suspected IUGR, breech babies or placental location, although are acknowledged to be imprecise, especially in weight estimation.

Routine Third Trimester Ultrasounds
Ultrasound examinations performed during the third trimester as routine screening in pregnancies without a specific medical concern or indication (BRICKER ET AL., 2015; ACOG, 2017B).

Medically Indicated Ultrasounds
An ultrasound performed to answer a specific clinical question or evaluate a suspected problem, rather than as routine screening (ACOG, 2017A; ACOG, 2017B). Examples include suspected fetal growth restriction, breech presentation, and placental concerns. (ACOG, 2021A; ACOG, 2021B; ACOG, 2019; ACOG, N.D.).

Fundal Height
The distance from the pubic bone to the top of the uterus, measured during prenatal visits. Fundal height measurements are used to screen a baby’s size and growth during pregnancy (ACOG, 2025A; ACOG, 2025B).

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).

Fetal Growth Restriction (IUGR, IGR or FGR)
A baby who is measuring smaller than expected for gestational age and it is suspected that the baby is not fulfilling its growth potential because of an underlying pathological condition (ACOG, 2021A; SMFM, 2020).

SGA (Small for Gestational Age)
A baby born weighing below the 10th percentile for their gestational age; SGA describes the baby’s size and does not necessarily mean that growth was pathologically restricted (ACOG, 2021; RCOG, 2024).

Both the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO) do not recommend or recommend against routinely performing third-trimester ultrasounds in uncomplicated pregnancies because current evidence has not shown that this practice improves maternal or fetal outcomes (ACOG, 2016; BRICKER ET AL., 2015; WHO, 2016).

Instead, ultrasounds after the anatomy scan, should be reserved for pregnancies with a specific medical indication, such as suspected fetal growth restriction, abnormal fundal-height measurements, maternal medical conditions, abnormal fetal presentation, or other clinical concerns (ACOG, 2016). This recommendation is based on randomized trials and systematic reviews (BRICKER ET AL., 2015). At the same time, ACOG notes that routine screening increases the detection of suspected abnormalities, which can lead to additional surveillance, labor induction, and cesarean birth without clear evidence of benefit (ACOG, 2016). Because of these considerations, ACOG recommends a selective, indication-based approach rather than universal routine screening (ACOG, 2016; ACOG, 2017A).

“Ultrasonography... should be used prudently and only when use is expected to answer a relevant clinical question or otherwise provide medical benefit to the patient” (ACOG, 2017A).

This systematic review and meta-analysis included 13 randomized controlled trials involving 34,980 women and compared routine ultrasound after 24 weeks with ultrasound performed only for clinical indications. It evaluated whether routine scanning improved neonatal outcomes or affected intervention rates (BRICKER ET AL., 2015).

Routine late ultrasound did not reduce perinatal mortality or preterm birth or demonstrate an overall benefit for mothers or babies. Pooled trials found no statistically significant overall differences in induction or cesarean births, although induction rates varied considerably between studies—an important contextual concern (BRICKER ET AL., 2015).

This trial was a large randomized controlled trial conducted to analyze routine obstetric ultrasounds. The study included 15,151 low-risk pregnant women from 109 U.S. practices. Women were randomly assigned to receive routine ultrasound examinations at 15–22 weeks and again at 31–35 weeks, or to receive ultrasounds only when there was a medical indication (EWIGMAN ET AL., 1993).

Routine third-trimester ultrasound detected additional fetal abnormalities but did not reduce perinatal mortality or serious neonatal illness or improve overall pregnancy outcomes compared with selective ultrasound for clinical indications. This landmark trial was later included in the 2015 Cochrane review and helped inform ACOG guidance for low-risk pregnancies (EWIGMAN ET AL., 1993; BRICKER ET AL., 2015; ACOG, 2016).

Author’s contextual analysis: Care provided within a clinical trial may differ from routine care because trial clinicians are aware that outcomes are being observed. Practices also vary in their guidelines and rates of induction and planned cesarean, as seen in the trials included in this review. Families should therefore consider that these pooled results may not translate directly to every real-world clinical setting.

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 here.

"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)

Author: Despite substantial uncertainty in ultrasound predictions and induction benefits, suspected macrosomia may still prompt an offer or recommendations for induction or cesarean birth.

Incorrect Diagnosis of a “Big Baby”: When specifically looking at retrospective evidence (studies and trials) of babies who were all labeled prenatally big for gestational age, we see incorrect labelling in 31 - 60% of mothers.

Studies show margins of errors ranging from 31% to 65% when diagnosing fetal weight (LOPIAN ET AL., 2026). In the big baby trial 60% of diagnosed big babies were falsely diagnosed and not large at birth (GARDOSI ET AL., 2025).

Detection Impact: Evidence shows us that detection of a big baby does increase interventions. When comparing babies who were undetected but large to babies suspected and large, there is no improved outcome for detected babies. Actually, some observational evidence shows an increase in adverse newborn outcomes with detection of a big baby. Increased interventions include inductions, planned & intrapartum cesareans.

Cesareans After Detection for a Large Baby: Cesareans (planned and intrapartum) went up after detection of big babies, even for those detected but not actually large at birth (LOPIAN ET AL., 2026).

Induction After Detection of a Large Baby & Impact on Cesarean Rates: Observational studies comparing true spontaneous labor compared with induction in babies suspected and large for gestational age, we see an increase in cesarean rates with induction (FRIESEN ET AL., 1995; BADR ET AL., 2024). Other observational & trial evidence comparing early induction with a mix of later inductions mixed with some spontaneous labors, shows a decrease in cesareans with earlier inductions (GARDOSI ET AL., 2025).

Induction After Detection & Impact on Perineal Tearing: Trials show an increase in tearing when evaluating mothers who were induced early for a suspected large baby (GARDOSI ET AL., 2025).

Induction After Detection of Large Babies & Shoulder Dystocia: Like cesareans, evidence is mixed. Observational induced vs spontaneous labor shows no difference or more dystocia’s with induced labors (FRIESEN ET AL., 1995; BADR ET AL., 2024). Trials and studies that compare early induction with later births not excluding inductions show a slight decrease in dystocia’s with an earlier induction (GARDOSI ET AL., 2025). Again, there are no trials comparing only spontaneous with induction to be able to evaluate those shoulder dystocia rates.

Induction After Detection of Large Babies & Adverse Outcomes for Babies: There is no overall proven benefit to adverse neonatal outcomes for inducing for a big baby (GARDOSI ET AL., 2025; LOPIAN ET AL., 2026; BADR ET AL., 2024)

“When Ultrasound Predicts a Big Baby”

If fundal-height measurement suggests that a baby may be small, ACOG recommends ultrasound assessment. An estimated fetal weight or abdominal circumference below the 10th percentile meets ACOG’s definition of fetal growth restriction but does not automatically require induction. Further surveillance, umbilical-artery Doppler assessment, and sometimes serial growth scans help distinguish a constitutionally small baby from pathological growth restriction and guide delivery timing (ACOG, 2021A; ACOG, 2025B).

“An additional challenge is the difficulty in differentiating between the fetus that is constitutionally small and fulfilling its growth potential and the small fetus that is not fulfilling its growth potential because of an underlying pathologic condition” (ACOG, 2021A).

In the Monier study, approximately half of babies suspected of growth restriction were not small at birth, while 78% of actually small babies were missed (MONIER ET AL).

Suspicion of small baby or IUGR was associated with more medically initiated early deliveries, without better neonatal outcomes among small babies. IRIS found that routine ultrasound improved detection (32% vs 19%) but also increased false alarms and inductions, without reducing severe complications or deaths around birth (1.7% vs 1.8%). Together, these studies show that detecting more suspected growth problems does not necessarily improve outcomes & is associated with more interventions (MONIER ET AL.; HENRICHS ET AL., 2019).

This systematic review found ultrasound estimates of fetal weight have a recognized margin of error, with errors greater than 10% occurring in some studies. The largest reported mean percentage error was an overestimation at 22.16% (MILNER & AREZINA, 2018).

Author’s consideration: This uncertainty is relevant when weighing the potential benefits and risks of interventions based on estimated fetal size.

Example: 10 lb estimated weight ÷ 1.2216 = 8.19 lb actual weight. A difference of approximately 1 pound 13 ounces & now within normal ranges.

In a randomized trial of 2,834 singleton pregnancies, five scheduled examinations combining ultrasound imaging and continuous-wave Doppler, performed between 18 and 38 weeks, were associated with a 35% relative increase in birthweight below the 10th percentile compared with a single imaging ultrasound at 18 weeks. Because the intensive protocol combined imaging and Doppler, the trial cannot determine whether either component—or their repeated combination—accounted for the finding. The authors acknowledged chance could be a possible explanation. The trial therefore presents a safety signal concerning repeated combined exposure; however, it does not prove that routine obstetric ultrasound causes fetal growth restriction (NEWNHAM ET AL., 1993).

Japan: National prenatal-care guidance includes third-trimester ultrasound examinations, with one scan between 24–35 weeks and another at 36 weeks or later. Actual scanning practices may vary by provider and clinical circumstances (MHLW, 2015).

Finland: Routine ultrasound screening is offered around 12–13 weeks and 20–21 weeks. Third-trimester ultrasounds are not part of universal screening and are generally performed when clinically indicated (HUS, 2026).

Norway: Routine ultrasounds are offered at 11–14 weeks and 17–19 weeks. Third-trimester ultrasounds are not routinely offered in uncomplicated pregnancies but may be performed when medically indicated (OUH, 2025).

These countries were selected for their comparatively strong maternal and neonatal outcomes (OECD, 2025) and their differing approaches to third-trimester ultrasound use. These comparisons illustrate variations in maternity care practices, rather than establishing that ultrasound frequency directly influences birth outcomes.

These countries were selected for their strong maternal and neonatal outcomes (OECD, 2025) and the availability of clear, moderate- to high-confidence ultrasound practice findings (GOI, N.D.; OUH, 2025).

Healthcare systems may influence ultrasound use. Official guidelines do not always reflect routine practice, which may also be shaped by how maternity care is funded, provider incentives, access to imaging, malpractice concerns, and local medical culture. For this reason, differences between countries cannot be attributed to guidelines—or healthcare outcomes—alone.

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.