A growth scan checks how your baby is growing, while Doppler ultrasound looks at blood flow between the placenta and baby. Here is what these scans can tell you and what happens when a baby measures small.
Pregnancy scans do more than provide a picture of your baby. At different stages of pregnancy, ultrasound can answer very different questions.
A growth scan is mainly used to assess how your baby is growing. It looks at measurements such as the baby's head, abdomen and thigh bone and uses these measurements to estimate fetal weight.
A Doppler ultrasound looks at blood flow. Depending on the clinical situation, it can help doctors assess circulation in vessels such as the umbilical artery and understand how the placenta and baby are functioning.
These two assessments are often discussed together, particularly when there is concern that a baby may be smaller than expected or that the placenta may not be working as well as it should.
But there is an important point that parents sometimes miss:
A baby measuring small does not automatically mean that something is wrong.
Some babies are simply constitutionally small. Others may have fetal growth restriction (FGR), where the baby has not reached its expected growth potential because of an underlying problem.
Understanding that difference is one of the main reasons growth is followed over time.
A growth scan is an ultrasound examination used to assess fetal growth and development later in pregnancy.
During the scan, the sonologist or fetal medicine specialist takes several measurements of the baby. These commonly include:
The measurements are compared with expected values for the baby's gestational age.
Importantly, the estimated weight shown on the scan is not the baby's actual weight. It is a calculated estimate based on ultrasound measurements.
Fetal growth assessment is also more meaningful when measurements are considered over time. A single scan provides a snapshot; sequential assessments can show whether the baby is following an expected growth pattern.
Not every pregnant woman needs the same number of growth scans.
A growth scan may be recommended when your obstetrician or fetal medicine specialist wants to check fetal growth more closely. This can happen for several reasons, including:
The timing and frequency depend on the individual pregnancy. There is no single schedule that applies to everyone.
The scan does not simply ask, “How much does the baby weigh?”
It looks at several measurements because fetal growth is a pattern rather than one number.
Measurements of the baby's head help assess growth of the skull and brain.
The abdominal circumference is particularly useful when assessing fetal size and growth. Changes in abdominal growth can sometimes provide important clues about fetal growth restriction.
The length of the thigh bone is another measurement used in fetal biometry.
The measurements are combined using an ultrasound formula to calculate an estimated fetal weight (EFW).
The result is then compared with reference values for the baby's gestational age.
You may see a percentile written on your ultrasound report, such as the 10th, 25th, 50th or 75th percentile.
A percentile compares the baby's estimated size with babies of the same gestational age in the reference population used by the reporting system.
For example, a baby around the 50th percentile is close to the middle of that reference range.
A lower percentile does not automatically mean that the baby is unhealthy.
This is where the distinction between small for gestational age (SGA) and fetal growth restriction (FGR) becomes important.
A baby may be considered small for gestational age when measurements such as estimated fetal weight or abdominal circumference fall below a particular percentile, commonly the 10th percentile.
But SGA and FGR are not interchangeable terms.
Some babies are naturally small and remain healthy. In other pregnancies, a smaller size reflects a problem with the baby's growth potential, often related to placental function.
Fetal growth restriction refers to a situation in which the fetus has not achieved its expected growth potential because of a pathological process.
That distinction is why doctors do not diagnose FGR simply by looking at one number. Growth pattern, Doppler findings and the wider clinical picture matter.
There is no single cause of fetal growth restriction.
One important factor is placental insufficiency, where the placenta is not delivering oxygen and nutrients as effectively as expected.
Other factors can include:
Sometimes, despite appropriate investigation, a single clear cause is not identified.
This is one reason fetal growth monitoring needs to be individualized rather than based only on the estimated fetal weight.
A Doppler ultrasound is a specialized form of ultrasound used to assess blood flow.
Instead of only producing an anatomical image, Doppler evaluates movement of blood through vessels.
Different Doppler techniques can provide information about blood flow, including spectral Doppler and colour flow imaging.
In pregnancy, Doppler assessment can be particularly useful when there is a concern about fetal growth or placental function.
Doppler can provide information about the circulation between the mother, placenta and baby.
When a baby is suspected to have fetal growth restriction, the umbilical artery Doppler is particularly important in many clinical protocols.
It can help doctors assess resistance to blood flow through the placenta and determine how closely the pregnancy may need to be monitored.
In pregnancies complicated by FGR, guidelines recommend serial Doppler assessment of the umbilical artery as part of fetal surveillance, with the frequency depending on the severity and Doppler findings.
Doppler is therefore not simply another measurement of the baby's size. It answers a different question.
Growth scan: How is the baby growing?
Doppler: What does the blood flow tell us about the circulation supporting the baby?
The vessel examined depends on the clinical question.
The umbilical artery carries blood from the fetus toward the placenta.
Umbilical artery Doppler is particularly important when fetal growth restriction is suspected because it can provide information about placental resistance.
The middle cerebral artery is a blood vessel in the baby's brain.
In selected situations, its blood-flow pattern may provide additional information about fetal circulation.
Uterine artery Doppler assesses blood flow in the maternal vessels supplying the uterus and placenta.
It may be useful in particular pregnancy assessments, depending on the clinical context.
The ductus venosus is a fetal blood vessel that connects with the fetal circulation near the heart.
Assessment of this vessel is relevant in selected high-risk situations, although Doppler protocols vary according to the clinical indication and guideline being followed.
Not every pregnancy requires assessment of all these vessels.
Not necessarily.
A Doppler result needs to be interpreted according to which vessel was examined, the gestational age, the specific Doppler measurement and the rest of the pregnancy assessment.
An abnormal result may mean that closer monitoring is needed. It does not, by itself, tell the entire story.
This is particularly important when parents see a result on a report and try to interpret it without the surrounding clinical information.
Your doctor may compare:
The next step is based on the complete picture.
There is a close relationship between fetal growth and placental blood flow.
When the placenta is not functioning normally, the baby may receive less oxygen and nutrients than expected. The baby may then show slower growth.
Doppler can sometimes identify changes in circulation associated with placental dysfunction.
This makes Doppler particularly useful when FGR has been diagnosed or is strongly suspected. However, Doppler is not a standalone test for diagnosing FGR.
A baby can be small with a reassuring Doppler, and Doppler findings may change the way a pregnancy with growth restriction is monitored.
Hearing that your baby is “small” can understandably cause concern.
But a small measurement is not automatically a diagnosis of fetal growth restriction.
Your doctor may first look at:
Sometimes the appropriate next step is simply to repeat the growth assessment after an interval.
In other pregnancies, additional surveillance may be needed.
Fetal growth is dynamic.
A single ultrasound cannot tell your doctor exactly how quickly your baby is growing.
If a baby measures smaller than expected, a repeat scan can show whether growth continues along a similar trajectory or whether there has been a change.
This is particularly useful because growth velocity can provide information that a single measurement cannot.
The interval between scans matters too. Performing growth scans too close together may not provide a meaningful indication of growth because ultrasound measurements themselves have a margin of error.
Your doctor therefore chooses the timing based on the pregnancy and the reason for monitoring.
No.
A growth scan provides an estimated fetal weight, not an exact measurement.
Ultrasound-based fetal weight calculations have inherent limitations, and the estimated weight can differ from the baby's actual birth weight.
For this reason, doctors usually use the estimated weight as one piece of clinical information rather than treating it as an exact prediction.
A scan saying that a baby weighs a particular amount does not mean the baby will be born at precisely that weight.
| Growth Scan | Doppler Scan |
|---|---|
| Assesses fetal size and growth | Assesses blood flow |
| Measures fetal body parts | Measures blood-flow characteristics |
| Calculates estimated fetal weight | Provides information about circulation |
| Helps assess growth pattern | Helps assess placental/fetal circulation |
| Useful when growth is a concern | Particularly useful in selected high-risk pregnancies |
| Can be repeated to monitor growth | May be repeated to monitor changes in blood flow |
Growth Scan: Assesses fetal size and growth
Doppler Scan: Assesses blood flow
Growth Scan: Measures fetal body parts
Doppler Scan: Measures blood-flow characteristics
Growth Scan: Calculates estimated fetal weight
Doppler Scan: Provides information about circulation
Growth Scan: Helps assess growth pattern
Doppler Scan: Helps assess placental/fetal circulation
Growth Scan: Useful when growth is a concern
Doppler Scan: Particularly useful in selected high-risk pregnancies
Growth Scan: Can be repeated to monitor growth
Doppler Scan: May be repeated to monitor changes in blood flow
Growth scan vs Doppler: what is the difference?
The two tests can complement one another, but they are not interchangeable.
No.
Fetal growth restriction is assessed using fetal biometry and the overall clinical picture. Doppler can provide important additional information, especially about placental and fetal circulation.
In other words, Doppler helps answer:
“How is the circulation supporting this baby?”
The growth scan helps answer:
“How is this baby growing?”
Putting those findings together gives the doctor a much clearer picture than either measurement alone.
The next step depends on several factors.
There is no single treatment plan for every pregnancy with FGR.
Monitoring may include:
The aim is to balance the risks of continuing the pregnancy against the risks associated with delivering too early.
The exact approach depends on gestational age, fetal growth, Doppler findings, fetal wellbeing and maternal condition. Professional guidelines differ in some details, so management is individualized.
No.
The severity and significance of FGR vary from one pregnancy to another.
Some babies with restricted growth remain stable with monitoring for a considerable period. In other pregnancies, worsening Doppler findings or other concerns may require more intensive surveillance or earlier delivery.
This is why doctors do not make decisions based solely on the baby's estimated weight.
A small baby with reassuring findings may be managed very differently from a baby with evidence of significant placental dysfunction.
Some babies who measure small during pregnancy are constitutionally small and continue to grow normally.
Others may have genuine growth restriction and require closer surveillance.
Whether a baby continues to grow appropriately depends on the underlying reason for the small measurements and how the pregnancy progresses.
That is why trend matters.
A sequence of appropriately timed growth scans can be more informative than one isolated measurement.
Fetal growth is influenced by many factors, including:
Sometimes a baby's size simply reflects familial or constitutional characteristics.
A smaller baby therefore should not automatically be assumed to have a disease.
Fetal growth restriction can present at different stages of pregnancy.
Early-onset FGR develops earlier in pregnancy and may be associated with more significant placental or fetal problems.
Late-onset FGR occurs later in pregnancy and can be more subtle. A baby may not appear dramatically small, which is one reason clinical assessment and appropriate surveillance remain important.
The distinction is based on gestational age and clinical criteria, rather than simply whether the baby appears small on ultrasound.
Not necessarily.
The need for Doppler depends on why the baby is measuring small and what other findings are present.
Your doctor may consider:
If there is a concern about fetal growth restriction, Doppler may become an important part of monitoring.
The appropriate test should be based on the clinical situation rather than performed simply because the baby is below an arbitrary number.
There is no universal schedule.
A woman with a pregnancy that is considered high risk may require additional scans, but the timing depends on the reason for the increased risk.
For example, monitoring may be different for:
If FGR has been diagnosed, professional guidance commonly recommends serial monitoring, including umbilical artery Doppler at intervals determined by the clinical findings.
Your obstetrician or fetal medicine specialist can determine the appropriate schedule for your pregnancy.
The examination is performed using ultrasound.
You will generally lie on an examination couch while the ultrasound probe is moved over your abdomen with ultrasound gel.
The clinician takes the necessary fetal measurements and may assess:
The exact components depend on why the scan has been requested.
You may hear Doppler sounds during the examination. These sounds represent blood-flow information and are not the baby's heartbeat being “recorded” in the way a conventional audio recording works.
Ultrasound does not use ionizing radiation.
Diagnostic ultrasound is widely used during pregnancy when medically indicated. Doppler is also an ultrasound-based technique.
As with any medical examination, ultrasound should be used appropriately and for a clinical purpose, with the examination performed by trained professionals.
No.
A growth scan is designed primarily to assess fetal growth and related findings. It is not a substitute for every other pregnancy screening or diagnostic test.
Depending on the stage of pregnancy and the clinical situation, different examinations may be used to assess:
A normal growth scan therefore does not mean that every possible fetal or maternal condition has been excluded.
A fetal medicine consultation may be considered when there is a specific concern about fetal growth, Doppler findings or another pregnancy-related issue.
Examples include:
A specialist can review the scan alongside previous measurements and the clinical history rather than interpreting one number on its own.
If you have been told that your baby is small or that Doppler monitoring is needed, it can help to ask specific questions.
For example:
Having these answers can make the report much easier to understand.
One of the most important things to remember is that fetal growth is a process, not a single measurement.
A baby who measures on the smaller side may be perfectly healthy.
Another baby with a similar estimated weight may need closer monitoring because the growth pattern, Doppler findings or other clinical features are different.
That is why fetal medicine specialists look at the whole picture.
Growth measurements tell us about size. Doppler adds information about circulation. Serial assessments show how things are changing.
Together, these findings can help guide appropriate monitoring during pregnancy.
Being told that your baby is “small” can be unsettling, especially when the ultrasound report contains numbers and terms that are difficult to interpret.
Try not to judge the result from the estimated weight or percentile alone.
A fetal growth assessment is most useful when the measurements are interpreted in context. Your doctor may look at previous scans, growth trends, Doppler blood flow, amniotic fluid, maternal health and other findings before deciding whether further monitoring is needed.
If your pregnancy requires a growth scan or Doppler assessment, the purpose is not simply to produce another set of numbers. These examinations help your care team understand how your baby is growing and, when necessary, whether the circulation supporting the baby needs closer observation.
For patients seeking fetal medicine consultation and pregnancy scan services in Trichy, Trichy Fetal Medicine and Fertility Centre provides services including growth scans with Doppler, fetal echocardiography, anomaly scans, NIPT, genetic counselling and other fetal medicine services.
To arrange this at our Trichy centre, see growth scan with Doppler; if you are unsure whether you need it, our doctors can tell you after a review.
This guide is for general information and does not replace a consultation with a fetal medicine specialist.
In line with the PCPNDT Act, we do not perform or support sex determination.
Growth Scan with Doppler
A scan that tracks your baby's growth and blood flow, especially important in the later months.
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