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 (LGA or Large for Gestational Age)
A term used to describe a baby with an unusually high birth weight, regardless of gestational age (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 birth, 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 below.

"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)

This Study compares interventions based off prenatal diagnosis

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.

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.

Shoulder dystocia diagnosis in this trial was not clarified. We do know the primary criteria was failure of gentle traction and the need for additional maneuvers, however we do not know how long providers allowed before stepping in and using maneuvers. We also know that the diagnosis of a big baby, as seen in Lopain, may increase diagnosis of shoulder dystocia. Also these physicians all practice under RCOG guidelines which do not encourage waiting for another contraction despite trials showing us that its common for a normal sized baby to need a fresh contraction (LOCATELLI ET AL., 2011) and this 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.

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).

This population-based study examined 14,100 singleton births. Whether or not a baby was ultimately born small for gestational age, those suspected of fetal growth restriction before birth were at least, approximately four times as likely to be born preterm, require resuscitation, or be admitted to a neonatal unit. Most additional preterm births followed induction or planned cesarean birth. Because this was observational, it cannot prove that the diagnosis caused these outcomes (MONIER ET AL., 2015).

This Dutch trial included 13,046 low-risk pregnancies recruited through 60 midwifery practices. Two routine growth scans increased prenatal detection of babies ultimately born small for gestational age from 19% to 32%, but also increased false-positives from 3.1% to 10.2%. Induction increased from 13.7% to 15.9%, while severe perinatal outcomes remained similar at 1.8% versus 1.7%. The routine-scan group averaged 2.04 third-trimester scans compared with 0.88 under usual care, meaning usual care did not represent “no ultrasound.” The trial was pragmatic and unblinded (HENRICHS ET AL., 2019).

There is currently little to no high-quality evidence that increasing prenatal detection of small babies through routine sizing ultrasounds improves severe neonatal outcomes. Some smaller trials may demonstrate lower NICU rates with additional scans, but neonatal outcomes were ultimately not improved. However, due to size & bias potential these trials are not considered high-quality evidence. There was a small Portuguese trial - Ratio 37 that indicated doppler ultrasounds evaluating placental & cord functions compared to routine growth scans checking size, may improve outcomes (RATIO37 STUDY GROUP, 2024). However, more research is needed.

Ultrasound estimates of fetal weight have a recognized margin of error, with errors greater than 10% occurring in some studies (MILNER & AREZINA, 2018).

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

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: Third trimester ultrasounds are commonly recommended, around 28-31 weeks (moderate-confidence finding) (GOI, N.D.)

Norway: Third trimester ultrasounds are more routine, only used when clinically indicated (high-quality finding) (OUH, 2025)

Finland: Third trimester ultrasounds are more routine, only used when clinically indicated (high-confidence finding) (OUH, 2025)

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.