When to Order Imaging for Growth Disturbances–Risk of Fetal Growth Restriction: ACR Appropriateness Decoded
You’re evaluating a pregnant patient with concerns for a growth disturbance. The fundal height is less than expected for gestational age, and you need to determine if this represents true Fetal Growth Restriction (FGR), a condition associated with significant perinatal morbidity and mortality. The key questions are which ultrasound studies are necessary now, and which are reserved for follow-up or higher-risk scenarios. Differentiating between a constitutionally small fetus and one with pathologic growth restriction is critical, and ordering the right initial and subsequent imaging is the first step. This guide outlines the American College of Radiology (ACR) Appropriateness Criteria to help you navigate these decisions with confidence, ensuring the right information is gathered without unnecessary studies.
What Does ACR Growth Disturbances–Risk of Fetal Growth Restriction Cover?
This ACR topic provides guidance for imaging evaluation in pregnancies where there is a suspicion or confirmed diagnosis of fetal growth restriction. The criteria address three common clinical situations: the initial evaluation of a pregnancy at low risk for FGR, the initial evaluation of a pregnancy at high risk for FGR, and the follow-up evaluation once FGR has been established. FGR is typically defined as an estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age.
These guidelines are specifically for assessing fetal size and well-being in the context of potential growth abnormalities. They do not cover routine anatomic surveys, evaluation for fetal anomalies unrelated to growth, or the management of other pregnancy complications like preeclampsia, although these conditions often coexist with FGR. The focus is strictly on using ultrasound to assess biometry, amniotic fluid, and fetal Doppler parameters to stratify risk and guide management in pregnancies affected by poor growth.
What Imaging Should I Order for Growth Disturbances–Risk of Fetal Growth Restriction? Recommendations by Clinical Scenario
The appropriate imaging pathway depends entirely on the patient’s risk profile and whether FGR is suspected or already diagnosed. The ACR provides clear recommendations for each context, primarily utilizing different applications of obstetric ultrasound.
For a patient with a suspected growth disturbance but at low risk for fetal growth restriction, the initial evaluation should begin with a standard transabdominal ultrasound of the pregnant uterus. This study is rated Usually appropriate and is sufficient to perform fetal biometry (to calculate an estimated fetal weight), assess amniotic fluid volume, and evaluate fetal anatomy. At this stage, various Doppler studies—including of the umbilical artery, middle cerebral artery (MCA), ductus venosus, and maternal uterine artery—are all considered Usually not appropriate. A biophysical profile (BPP) is also not indicated for this initial, low-risk assessment.
The recommendations change for the initial evaluation of a growth disturbance in a high-risk pregnancy. In this scenario, in addition to the standard transabdominal ultrasound for biometry, both a biophysical profile and a duplex Doppler ultrasound of the fetal umbilical artery are rated Usually appropriate. Umbilical artery Doppler velocimetry is a key tool for assessing placental function and is a critical component in the surveillance of suspected FGR. Doppler assessment of the maternal uterine artery and the ductus venosus May be appropriate depending on the specific clinical context and gestational age, as they can provide additional information about uteroplacental insufficiency and fetal cardiac function. Doppler of the fetal middle cerebral artery remains Usually not appropriate for the *initial* high-risk evaluation, as it is typically reserved for monitoring established FGR.
Once there is established fetal growth restriction requiring follow-up evaluation, a more comprehensive set of ultrasound studies becomes necessary. All of the following are rated Usually appropriate: transabdominal ultrasound for interval growth, biophysical profile for fetal well-being, and duplex Doppler of the fetal umbilical artery, middle cerebral artery, and ductus venosus. Serial assessment of these parameters is the standard of care for monitoring fetal status in FGR. MCA Doppler helps detect fetal brain-sparing, a sign of chronic hypoxia, while ductus venosus Doppler provides insight into fetal cardiac decompensation. Maternal uterine artery Doppler May be appropriate in some follow-up protocols but is not universally required.
ACR Imaging Recommendations Table
| Clinical Scenario | Top Procedure | ACR Rating | Adult RRL | Pediatric RRL |
|---|---|---|---|---|
| Growth disturbance. Low risk for fetal growth restriction. Initial evaluation. | US pregnant uterus transabdominal | Usually appropriate | O 0 mSv | O 0 mSv [ped] |
| Growth disturbance. High risk for fetal growth restriction. Initial evaluation. | US duplex Doppler fetal umbilical artery | Usually appropriate | O 0 mSv | O 0 mSv [ped] |
| Established fetal growth restriction. Follow-up evaluation. | US duplex Doppler fetal umbilical artery | Usually appropriate | O 0 mSv | O 0 mSv [ped] |
Adult vs. Pediatric Growth Disturbances–Risk of Fetal Growth Restriction Imaging: Radiation Dose Tradeoffs
In the context of fetal imaging, the “adult” refers to the pregnant patient, while the “pediatric” consideration applies to the fetus. The principle of As Low As Reasonably Achievable (ALARA) is paramount in obstetric imaging to minimize any potential risk to the developing fetus. Fortunately, for the evaluation of fetal growth restriction, ultrasound is the exclusive imaging modality recommended by the ACR. All listed procedures have a relative radiation level of zero (O 0 mSv).
This is a primary reason why ultrasound is the cornerstone of obstetric imaging. It uses non-ionizing sound waves to generate images and provides excellent real-time information without exposing the mother or fetus to radiation. Therefore, the traditional risk-benefit discussion regarding radiation dose tradeoffs, which is common in CT or nuclear medicine, does not apply here. The key considerations for fetal safety with ultrasound involve thermal and mechanical effects, which are managed by adhering to established output display standards and keeping examination times as short as necessary, particularly when using Doppler.
Imaging Protocol Details for Growth Disturbances–Risk of Fetal Growth Restriction
Once you’ve decided on the right study based on the clinical scenario, ensuring it is performed and interpreted correctly is the next critical step. Our protocol guides provide detailed, practical information on technique, required measurements, and interpretation principles for the studies recommended in these ACR criteria.
Tools to Help You Order the Right Study
Navigating imaging guidelines can be complex. GigHz offers a suite of tools designed to support evidence-based clinical decisions and streamline the ordering process.
For scenarios beyond fetal growth restriction, the ACR Appropriateness Criteria Lookup provides direct access to the full library of ACR guidelines, covering thousands of clinical variants across all specialties. This tool helps you quickly find the official recommendations for your patient’s specific presentation.
To ensure studies are performed to the highest standard, the Imaging Protocol Library offers detailed, step-by-step protocols for a wide range of imaging procedures, including the various obstetric ultrasounds discussed here. These guides are invaluable for trainees and for standardizing techniques across a department.
While not relevant for the ultrasound-based recommendations in this topic, the Radiation Dose Calculator is an essential resource for other clinical situations. It helps you estimate and track cumulative radiation exposure from medical imaging, facilitating informed conversations with patients about the risks and benefits of procedures involving ionizing radiation.
What is the difference between Fetal Growth Restriction (FGR) and Small for Gestational Age (SGA)?
Small for Gestational Age (SGA) is a descriptive term for a fetus with an estimated weight below a certain percentile (usually the 10th) for its gestational age. Fetal Growth Restriction (FGR), or Intrauterine Growth Restriction (IUGR), is a pathological condition where a fetus does not reach its genetically determined growth potential. While most FGR fetuses are SGA, not all SGA fetuses have FGR. Some are constitutionally small and healthy. The goal of imaging, particularly with Doppler studies, is to differentiate between these two conditions and identify the fetuses at high risk of adverse outcomes due to placental insufficiency.
Why is umbilical artery (UA) Doppler so important in high-risk and established FGR cases?
Umbilical artery (UA) Doppler velocimetry is a noninvasive method to assess placental function. It measures the resistance to blood flow in the placenta. In a healthy pregnancy, there is robust forward blood flow throughout the cardiac cycle. With increasing placental dysfunction, the resistance increases, leading to decreased, then absent, and finally reversed end-diastolic velocity (AREDV) in the umbilical artery. These findings are strongly associated with an increased risk of perinatal morbidity and mortality, and their presence guides critical management decisions, including the timing of delivery.
When should Middle Cerebral Artery (MCA) Doppler be performed?
Middle Cerebral Artery (MCA) Doppler is typically reserved for the follow-up and management of established FGR, not for initial screening. It is used to detect the “brain-sparing” phenomenon, a fetal adaptive response to chronic hypoxia. When the fetus is not receiving enough oxygen, it shunts blood preferentially to the brain, heart, and adrenal glands. This results in vasodilation in the MCA, which can be detected as an increased velocity of blood flow (specifically, a low pulsatility index). An abnormal MCA Doppler is a sign of significant fetal compromise.
What is the role of the biophysical profile (BPP)?
The biophysical profile (BPP) is a test of acute fetal well-being. It assesses five parameters: fetal breathing movements, gross body movements, fetal tone, amniotic fluid volume, and a non-stress test (NST). Each component is given a score of 0 or 2. A normal BPP score (8 or 10) is highly reassuring of fetal health, while a low score indicates potential fetal compromise and may prompt delivery. It is used in conjunction with growth assessment and Doppler studies to provide a comprehensive picture of fetal status in high-risk pregnancies, including those with FGR.
Are maternal uterine artery Dopplers useful in managing FGR?
Maternal uterine artery Doppler assessment is primarily used as a screening tool in the second trimester to predict the risk of developing preeclampsia and FGR later in pregnancy. High resistance (indicated by notching or an elevated pulsatility index) suggests impaired placentation. While it has high predictive value for these conditions, its role in the *management* of already established FGR is less clear, which is why the ACR rates it as “May be appropriate” rather than “Usually appropriate” for initial high-risk and follow-up evaluations. Its utility depends on institutional protocols and the specific clinical picture.
Frequently Asked Questions
What is the difference between Fetal Growth Restriction (FGR) and Small for Gestational Age (SGA)?
Small for Gestational Age (SGA) is a descriptive term for a fetus with an estimated weight below a certain percentile (usually the 10th) for its gestational age. Fetal Growth Restriction (FGR), or Intrauterine Growth Restriction (IUGR), is a pathological condition where a fetus does not reach its genetically determined growth potential. While most FGR fetuses are SGA, not all SGA fetuses have FGR. Some are constitutionally small and healthy. The goal of imaging, particularly with Doppler studies, is to differentiate between these two conditions and identify the fetuses at high risk of adverse outcomes due to placental insufficiency.
Why is umbilical artery (UA) Doppler so important in high-risk and established FGR cases?
Umbilical artery (UA) Doppler velocimetry is a noninvasive method to assess placental function. It measures the resistance to blood flow in the placenta. In a healthy pregnancy, there is robust forward blood flow throughout the cardiac cycle. With increasing placental dysfunction, the resistance increases, leading to decreased, then absent, and finally reversed end-diastolic velocity (AREDV) in the umbilical artery. These findings are strongly associated with an increased risk of perinatal morbidity and mortality, and their presence guides critical management decisions, including the timing of delivery.
When should Middle Cerebral Artery (MCA) Doppler be performed?
Middle Cerebral Artery (MCA) Doppler is typically reserved for the follow-up and management of established FGR, not for initial screening. It is used to detect the “brain-sparing” phenomenon, a fetal adaptive response to chronic hypoxia. When the fetus is not receiving enough oxygen, it shunts blood preferentially to the brain, heart, and adrenal glands. This results in vasodilation in the MCA, which can be detected as an increased velocity of blood flow (specifically, a low pulsatility index). An abnormal MCA Doppler is a sign of significant fetal compromise.
What is the role of the biophysical profile (BPP)?
The biophysical profile (BPP) is a test of acute fetal well-being. It assesses five parameters: fetal breathing movements, gross body movements, fetal tone, amniotic fluid volume, and a non-stress test (NST). Each component is given a score of 0 or 2. A normal BPP score (8 or 10) is highly reassuring of fetal health, while a low score indicates potential fetal compromise and may prompt delivery. It is used in conjunction with growth assessment and Doppler studies to provide a comprehensive picture of fetal status in high-risk pregnancies, including those with FGR.
Are maternal uterine artery Dopplers useful in managing FGR?
Maternal uterine artery Doppler assessment is primarily used as a screening tool in the second trimester to predict the risk of developing preeclampsia and FGR later in pregnancy. High resistance (indicated by notching or an elevated pulsatility index) suggests impaired placentation. While it has high predictive value for these conditions, its role in the *management* of already established FGR is less clear, which is why the ACR rates it as “May be appropriate” rather than “Usually appropriate” for initial high-risk and follow-up evaluations. Its utility depends on institutional protocols and the specific clinical picture.
Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 21, 2026
