A fetal growth ultrasound is an ultrasound examination used to assess how a baby is growing during pregnancy. It can help healthcare professionals measure the baby's size, estimate fetal weight, and look at development and other pregnancy findings.
Fetal growth changes throughout pregnancy, so ultrasound measurements are interpreted according to the baby's gestational age and previous measurements when available.
For a week-by-week overview of fetal development, visit our fetal growth by week guide.
What Is a Fetal Growth Ultrasound?
A fetal growth ultrasound uses sound waves to create images of the baby inside the uterus.
During the examination, the sonographer or healthcare professional may take several measurements of the fetus. These measurements can be compared with expected ranges for the baby's gestational age.
A growth ultrasound may provide information about:
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Fetal size
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Fetal growth pattern
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Estimated fetal weight
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Head size
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Abdominal size
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Femur length
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Amniotic fluid
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Placental location and appearance
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Fetal position
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Other features that may be clinically relevant
The exact assessment depends on the stage of pregnancy and the reason for the scan.
What Does a Fetal Growth Ultrasound Measure?
Several fetal measurements can be used to assess growth.
Head circumference
Head circumference measures the approximate circumference of the baby's head.
It is one of the measurements used when assessing fetal size.
Abdominal circumference
Abdominal circumference measures the baby's abdomen.
This measurement can be particularly useful when healthcare professionals are assessing fetal growth and estimated fetal weight.
Femur length
Femur length measures the baby's thigh bone.
It is another measurement used in fetal biometry.
Estimated fetal weight
Ultrasound measurements can be combined to calculate an estimated fetal weight.
It is important to understand that this is an estimate, not the baby's exact weight.
Why Might a Doctor Recommend a Growth Ultrasound?
Not every pregnancy requires repeated growth ultrasounds.
A healthcare professional may recommend additional monitoring when there is a clinical reason to assess fetal growth more closely.
Possible reasons can include:
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Concern that the baby may be smaller than expected
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Concern that the baby may be larger than expected
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Differences between expected and measured pregnancy size
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Certain maternal health conditions
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Previous pregnancy complications
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Abnormal findings during another examination
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Concerns about placental function
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Other pregnancy-related factors
The decision depends on the individual pregnancy.
When Is a Fetal Growth Ultrasound Done?
The timing of a growth ultrasound varies.
There is no single week that is appropriate for every pregnant person. Your obstetrician or healthcare provider may recommend a scan based on your pregnancy history, clinical findings, gestational age, and any concerns about fetal growth.
If more than one ultrasound is performed, comparing measurements over time can help doctors assess the baby's growth pattern.
How Is Fetal Growth Assessed?
Fetal growth is usually assessed using more than one piece of information.
A healthcare professional may consider:
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Pregnancy dating
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Previous ultrasound measurements
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Current fetal measurements
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Estimated fetal weight
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Growth percentile
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Amniotic fluid
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Placental findings
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Maternal health
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Other clinical findings
This is why a single ultrasound measurement should not be interpreted in isolation.
What Does “Measuring Small” Mean?
If a fetus measures smaller than expected, it does not automatically mean there is a serious problem.
There are several possible explanations.
For example:
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Pregnancy dates may be different from the estimated dates.
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The baby may naturally be smaller.
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Ultrasound measurements have limitations.
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Growth may need to be monitored over time.
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There may be an underlying pregnancy-related reason that requires assessment.
Your doctor may recommend another ultrasound or additional testing depending on the findings.
What Does “Measuring Large” Mean?
A fetus that measures larger than expected also does not automatically indicate a problem.
Normal differences in fetal size can occur.
The healthcare professional may consider the baby's measurements alongside pregnancy dating, maternal factors, previous scans, and other clinical information.
Further assessment may be recommended if the measurements consistently suggest that the baby is significantly larger than expected.
Can Ultrasound Predict the Baby's Exact Weight?
No.
Ultrasound can provide an estimated fetal weight, but it cannot determine the baby's exact weight before birth.
The estimate is calculated using fetal measurements and mathematical formulas.
There can be a difference between the estimated weight on ultrasound and the baby's actual birth weight.
For this reason, doctors generally consider the estimated weight together with the overall clinical picture.
Is Fetal Growth the Same Every Week?
No.
Fetal development is continuous, but the rate and type of growth change throughout pregnancy.
Early pregnancy is characterized by rapid formation and development of major structures.
During the second and third trimesters, the baby continues developing while increasing in length and weight. Organ maturation and accumulation of body fat become increasingly important later in pregnancy.
You can follow these changes in our fetal growth by week guide.
Fetal Growth Ultrasound vs Routine Pregnancy Ultrasound
These terms can sometimes be confusing.
A routine pregnancy ultrasound may be performed for several reasons, including confirming pregnancy dating, assessing fetal anatomy, checking fetal position, or evaluating other pregnancy findings.
A fetal growth ultrasound places particular emphasis on fetal measurements and growth assessment.
The exact purpose of an ultrasound depends on why it has been requested and the stage of pregnancy.
What Happens During a Growth Ultrasound?
A typical ultrasound is non-invasive.
Depending on the stage of pregnancy and the type of examination, the healthcare professional may:
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Ask you to lie on an examination bed
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Apply ultrasound gel to your abdomen
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Move an ultrasound probe over the abdomen
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Obtain images of the fetus
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Take fetal measurements
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Assess other relevant pregnancy findings
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Record measurements for clinical interpretation
The procedure is generally straightforward and does not involve radiation.
Can a Growth Ultrasound Detect Fetal Growth Problems?
Ultrasound can help identify measurements that are smaller or larger than expected and can help doctors monitor growth over time.
However, an ultrasound alone does not diagnose every possible pregnancy problem.
If a growth concern is identified, your healthcare provider may recommend additional ultrasound examinations, Doppler studies, monitoring, or other tests depending on the situation.
What Is a Growth Percentile?
A fetal growth percentile compares a baby's measurement or estimated weight with measurements from other pregnancies at a similar gestational age.
For example, a measurement near the middle of the reference range would be around the 50th percentile.
A percentile is not a grade.
A baby does not necessarily need to be exactly at the 50th percentile to be healthy.
Doctors look at the overall pattern and clinical circumstances when interpreting fetal growth.
Why Are Repeat Growth Ultrasounds Sometimes Needed?
One ultrasound provides information at one point in time.
A repeat ultrasound can show whether the baby is continuing to grow.
Comparing measurements from different scans may help healthcare professionals understand whether fetal growth is:
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Continuing as expected
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Increasing more slowly
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Increasing more rapidly
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Remaining consistent with the baby's previous growth pattern
The timing between scans depends on the clinical reason for monitoring.
Fetal Growth by Week
Fetal size and development change substantially from the early weeks through the third trimester.
A week-by-week guide can help you understand common developmental milestones, including changes in:
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Fetal length
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Fetal weight
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Brain development
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Organ development
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Body proportions
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Movement
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Physical features
Read our complete fetal growth by week guide to explore pregnancy development week by week.
You can also use our pregnancy calculator to estimate your pregnancy week and due date.
Frequently Asked Questions
What is a fetal growth ultrasound?
A fetal growth ultrasound is an ultrasound examination that focuses on assessing fetal size and growth using measurements such as head circumference, abdominal circumference, and femur length.
Is a fetal growth ultrasound safe?
Ultrasound uses sound waves rather than ionizing radiation. It has been widely used in pregnancy when medically indicated.
Can a growth ultrasound tell me how much my baby weighs?
It can provide an estimated fetal weight, but the estimate is not the same as an exact measurement of the baby's weight.
What if my baby is measuring a week behind?
A baby measuring a little behind does not automatically mean there is a problem. Pregnancy dating, natural variation, measurement differences, and growth patterns all need to be considered by your healthcare provider.
What if my baby is measuring ahead?
Measuring ahead does not automatically indicate a problem. Your doctor may consider pregnancy dates, fetal measurements, maternal factors, and previous ultrasound results.
How often do I need a fetal growth ultrasound?
There is no standard schedule for everyone. Your healthcare provider will decide whether another scan is needed based on your individual pregnancy.
Does a fetal growth ultrasound show the baby's development?
Yes. Depending on the type and timing of the ultrasound, it can provide information about fetal anatomy, measurements, movement, position, and other findings.
Final Takeaway
A fetal growth ultrasound is an important tool for monitoring fetal size and growth when additional assessment is needed. It can measure parts of the baby's body, estimate fetal weight, and help healthcare professionals follow growth over time.
An ultrasound measurement should always be interpreted in the context of gestational age and the overall pregnancy rather than as a single number.
For a detailed week-by-week pregnancy timeline, visit our fetal growth by week guide. You can also use our pregnancy calculator to estimate your current pregnancy week.