Author: UltraLog

Hearing that your baby is “measuring small” on ultrasound can be worrying.

You may be told that your baby’s estimated weight is below the 10th percentile and immediately wonder:

Does this mean my baby has IUGR?

Not necessarily.

A baby who is small for gestational age and a baby whose growth is truly restricted are not always the same thing.

Here is the difference between SGA (Small for Gestational Age) and FGR (Fetal Growth Restriction), previously commonly called IUGR.

What Is SGA?

SGA stands for Small for Gestational Age.

It generally describes a fetus whose estimated size or weight is small for the current gestational age, commonly below the 10th percentile.

But being small does not automatically mean that something is wrong.

Some babies are naturally small because of genetics or parental body size.

These babies may remain small throughout pregnancy while continuing to grow steadily. Their amniotic fluid and Doppler blood flow may also remain normal.

What Is FGR or IUGR?

FGR stands for Fetal Growth Restriction.

You may also hear the older term IUGR (Intrauterine Growth Restriction).

FGR means that the fetus may not be reaching its expected growth potential.

One important cause is placental insufficiency, in which the placenta may not provide the fetus with enough oxygen and nutrients to support optimal growth.

This is why doctors look at much more than fetal weight alone.

SGA vs FGR: What Is the Difference?

An easy way to understand the difference is:

SGA = The baby is small.

FGR = The baby’s growth may be restricted.

A fetus can be small and healthy.

On the other hand, fetal growth restriction is concerned not only with size, but also with how the baby is growing over time and whether there are signs of placental dysfunction.

How Does Ultrasound Help?

When a baby is measuring small, ultrasound assessment may include:

• Estimated Fetal Weight (EFW)
• Abdominal Circumference (AC)
• Head Circumference (HC)
• Femur Length (FL)
• Growth compared with previous examinations
• Amniotic fluid volume
• Placental assessment
• Umbilical Artery Doppler
• Middle Cerebral Artery (MCA) Doppler
• Cerebroplacental Ratio (CPR), when indicated

These findings help healthcare providers determine whether the baby is simply small or whether closer monitoring for fetal growth restriction is needed.

Why Is Abdominal Circumference Important?

Abdominal Circumference, or AC, is an important measurement when assessing fetal growth.

When placental function is impaired, fetal abdominal growth may be affected.

In some growth-restricted babies, the abdomen may therefore appear relatively smaller compared with other fetal measurements.

However, AC should never be interpreted in isolation. The overall growth pattern, fetal weight, Doppler findings and clinical situation all need to be considered together.

Does Below the 10th Percentile Always Mean Something Is Wrong?

No.

Being below the 10th percentile does not automatically mean that a baby is unhealthy.

Some babies are constitutionally small and continue to grow normally.

This is why the pattern of growth over time can be just as important as a single estimated fetal weight measurement.

Serial growth ultrasounds can help show whether the baby continues to grow along an expected pattern or whether growth is slowing.

What Happens If My Baby Is Measuring Small?

If your baby is measuring small, your healthcare provider may recommend additional growth ultrasounds and, when appropriate, Doppler studies.

The goal is not simply to determine how many grams the baby weighs.

The more important questions are:

Is the baby continuing to grow?

Is the placenta supporting the baby adequately?

Is the blood flow reassuring?

A small baby is not always a growth-restricted baby.

Regular monitoring helps healthcare providers distinguish between a healthy, naturally small fetus and a fetus that may require closer surveillance.

This article is for general pregnancy and ultrasound education and is not a substitute for individualized medical advice, diagnosis or treatment.

Wondering if your baby’s weight is normal? Learn the average fetal weight by week from 12 to 40 weeks, how ultrasound estimates fetal weight (EFW), and what normal growth looks like during pregnancy.
Fetal Weight by Week: Is My Baby Growing Normally?

One of the most common questions during pregnancy is:

“Is my baby’s weight normal?”

During routine prenatal ultrasounds, doctors estimate your baby’s weight using several body measurements. This estimate is called Estimated Fetal Weight (EFW).

The table below shows the approximate average fetal weight throughout pregnancy.

Average Fetal Weight by Week

Gestational Age	Average Weight
12 weeks	14 g
16 weeks	100 g
20 weeks	300 g
24 weeks	600 g
28 weeks	1,100 g
30 weeks	1,400 g
32 weeks	1,700 g
34 weeks	2,200 g
36 weeks	2,700 g
38 weeks	3,100 g
40 weeks	3,300~3,500 g

These values are averages. Every baby grows at a slightly different rate.

How Is Fetal Weight Estimated?

Ultrasound does not measure your baby’s weight directly.

Instead, it calculates an estimate using several fetal measurements, including:

• Biparietal Diameter (BPD)
• Head Circumference (HC)
• Abdominal Circumference (AC)
• Femur Length (FL)

These measurements are entered into validated formulas to calculate the Estimated Fetal Weight (EFW).

How Accurate Is Ultrasound Weight Estimation?

Many parents ask,

“Can ultrasound accurately predict my baby’s weight?”

The answer is mostly yes—but not perfectly.

Ultrasound estimates usually have an error range of ±10–15%.

For example, if the estimated weight is 2,000 g, the actual birth weight may reasonably range from about 1,700 to 2,300 g.

For this reason, healthcare providers focus more on your baby’s growth trend over time than on a single measurement.

What If My Baby Is Smaller Than Average?

A smaller-than-average baby is not always a cause for concern.

Possible reasons include:

• Family genetics
• Naturally small body size
• Normal variation in fetal growth

However, if growth slows significantly or blood flow abnormalities are detected, your doctor may evaluate for Fetal Growth Restriction (FGR/IUGR).

What If My Baby Is Larger Than Average?

A larger baby can also be completely healthy.

Sometimes, increased fetal weight may be associated with:

• Gestational diabetes
• Large for Gestational Age (LGA)
• Delivery planning considerations

Your healthcare provider will assess the overall clinical picture rather than fetal weight alone.

Frequently Asked Questions

Is 1 kg normal at 28 weeks?

Yes. Around 1,100 g is considered average at 28 weeks, so approximately 1 kg is often within the normal range depending on individual growth patterns.

My baby measures two weeks behind. Should I worry?

Not necessarily.

Doctors usually monitor growth over time rather than relying on a single ultrasound measurement.

Is ultrasound weight the same as birth weight?

No.

Estimated Fetal Weight (EFW) is an approximation and may differ from the baby’s actual birth weight.

Final Thoughts

Fetal weight is an important indicator of your baby’s development, but it is only one part of the overall assessment.

Doctors also evaluate fetal anatomy, amniotic fluid, placental function, blood flow, and the baby’s growth pattern over time.

Regular prenatal care and follow-up ultrasounds are the best ways to monitor your baby’s health.

Many expectant parents become nervous when the sonographer gently jiggles or taps the mother’s abdomen during a 3D ultrasound.

One of the most common questions is:

“Is my baby okay?”
“Does shaking my belly hurt the baby?”

The good news is that this gentle movement is a normal part of many 3D ultrasound examinations and is generally considered safe when performed by a trained healthcare professional.

Why Do We Gently Shake the Belly?

A 3D ultrasound depends on the baby’s position.

Sometimes the baby’s face is hidden because they are:

• Facing the placenta
• Resting against the uterine wall
• Covering their face with their hands or feet
• Sleeping in the same position

When this happens, the sonographer may gently jiggle the mother’s abdomen to encourage the baby to move just enough for a clearer view.

The goal is not to force the baby to move, but simply to create a small change in position.

How Much Movement Does the Baby Feel?

Many parents imagine that the baby is being shaken strongly.

In reality, the movement is usually very gentle.

I often explain it this way to my patients:

It is similar to the movement your baby experiences when you walk or climb a few stairs.

Babies naturally experience movement throughout pregnancy whenever the mother:

• Walks
• Changes position
• Rides in a car
• Goes about her normal daily activities

A gentle abdominal jiggle during a 3D ultrasound is generally no more intense than these everyday movements.

What If the Baby Still Doesn’t Move?

Some babies simply love to sleep.

Even after gentle stimulation, they may continue covering their face or remain in the same position.

In those situations, the sonographer may:

• Wait a few minutes
• Ask the mother to walk around briefly
• Change the mother’s position
• Schedule another attempt if needed

We do not keep shaking harder just to get a better picture.

Safety Always Comes First

Although parents enjoy seeing their baby’s face, the baby’s well-being is always the top priority.

A clear 3D image is wonderful, but it is never worth making the mother uncomfortable or using excessive pressure.

Every examination is performed with safety in mind.

Final Thoughts

If your sonographer gently shakes your belly during a 3D ultrasound, there’s usually no reason to worry.

In many cases, it’s simply a gentle technique to help your baby turn their face toward the ultrasound probe.

Sometimes it works.

Sometimes your little one decides to keep sleeping anyway—and that’s perfectly normal too.

If you are expecting identical twins who share one placenta, you may have heard of Twin-to-Twin Transfusion Syndrome (TTTS). This condition can sound frightening, but regular detailed ultrasound examinations allow specialists to detect it early and monitor your babies closely.

So, what exactly do sonographers look for during a detailed ultrasound?

What Is TTTS?

Twin-to-Twin Transfusion Syndrome (TTTS) is a complication that occurs only in monochorionic twin pregnancies, where both babies share a single placenta.

Tiny blood vessel connections within the placenta can cause blood to flow unevenly between the twins. As a result:

• The donor twin loses blood volume.
• The recipient twin receives too much blood.

Without treatment, TTTS can affect the health of both babies.

1. Confirming Chorionicity

The first step is determining whether the twins share one placenta.

TTTS develops only in monochorionic twins, making chorionicity the most important starting point of the examination.

2. Measuring Amniotic Fluid

One of the key ultrasound findings is the difference in amniotic fluid around each baby.

The sonographer measures the Deepest Vertical Pocket (DVP) for both twins.

Typical findings include:

• Donor twin: Very little amniotic fluid (oligohydramnios)
• Recipient twin: Excess amniotic fluid (polyhydramnios)

This imbalance is often the earliest sign of TTTS.

3. Evaluating the Bladder

The babies’ bladders provide important clues.

The donor twin may produce very little urine, causing the bladder to appear very small or even invisible during the examination.

The recipient twin often has a larger, well-filled bladder because increased blood flow leads to increased urine production.

4. Comparing Fetal Growth

Measurements are obtained for both babies, including:

• Biparietal Diameter (BPD)
• Head Circumference (HC)
• Abdominal Circumference (AC)
• Femur Length (FL)
• Estimated Fetal Weight (EFW)

Although growth differences do not confirm TTTS by themselves, they help distinguish TTTS from other complications such as selective fetal growth restriction (sFGR).

5. Performing Doppler Ultrasound

Blood flow is carefully assessed using Doppler ultrasound.

The following vessels are commonly evaluated:

• Umbilical Artery (UA)
• Middle Cerebral Artery (MCA)
• Ductus Venosus (DV)
• Umbilical Vein (UV)

Abnormal Doppler findings may indicate that TTTS has progressed and requires urgent evaluation.

6. Examining the Heart

The recipient twin’s heart works harder because of increased blood volume.

During the ultrasound, specialists evaluate:

• Heart size
• Cardiac function
• Valve regurgitation
• Signs of heart strain

Early detection of cardiac changes is essential for treatment planning.

7. Looking for Hydrops Fetalis

In severe cases, fluid may accumulate in different parts of the baby’s body.

The sonographer checks for:

• Ascites
• Pleural effusion
• Pericardial effusion
• Skin edema

These findings suggest advanced disease and require immediate medical attention.

What Is the Usual Ultrasound Checklist?

During a detailed ultrasound, specialists generally assess:

• Placental sharing (chorionicity)
• Amniotic fluid volume
• Fetal bladder
• Fetal growth
• Doppler blood flow
• Cardiac function
• Hydrops fetalis

Each step provides important information about the health of both babies.

Final Thoughts

TTTS is a serious but treatable complication when detected early.

Regular ultrasound surveillance is essential for monochorionic twin pregnancies because changes in amniotic fluid, blood flow, and fetal heart function may develop over time.

A detailed ultrasound is much more than simply seeing your babies’ faces—it is a comprehensive examination that helps protect both twins throughout pregnancy.

One of the most common questions sonographers hear during the anatomy scan is:

“Will we be able to see our baby’s face today?”

For healthcare professionals, the anatomy scan is a detailed medical examination. We carefully assess the baby’s brain, heart, spine, kidneys, limbs, and many other organs to ensure healthy development.

For parents, however, this appointment often means something much more personal.

It is the day they hope to truly “meet” their baby.

Seeing the Face Makes the Baby Feel Real

Although parents may have already felt kicks and seen previous ultrasound images, the baby’s face creates a completely different emotional connection.

Watching a baby yawn, suck a thumb, or make tiny facial expressions reminds parents that there is a little person growing inside the womb.

For many families, this is the moment pregnancy becomes even more real.

It Brings Comfort and Reassurance

Parents naturally want to know that their baby is growing well.

While sonographers evaluate the facial anatomy for medical reasons, many parents simply feel reassured when they can see their baby’s face.

Sometimes, just one clear image is enough to ease weeks of anxiety.

Everyone Starts Guessing the Family Resemblance

“She has Mom’s lips.”

“He looks just like Dad.”

These conversations often begin long before birth.

A single ultrasound image can spark excitement and strengthen the emotional bond between parents and their unborn baby.

Why Can’t We Always See the Baby’s Face?

This is probably the biggest disappointment for many parents.

The truth is that babies don’t always cooperate.

Your baby may be:

• Facing the mother’s back
• Covering the face with tiny hands
• Hidden behind the placenta or umbilical cord
• In a position that makes facial imaging difficult

The amount of amniotic fluid, gestational age, and maternal body habitus can also affect image quality.

Not seeing the face does not usually mean that something is wrong.

Sonographers Feel the Pressure Too

Many parents don’t realize that sonographers also hope to capture a beautiful face.

We know how much families are looking forward to that special moment.

But our first responsibility is to perform a thorough medical examination.

Sometimes we spend more time examining the baby’s heart or brain than trying to obtain the perfect facial image.

A healthy baby is always more important than the perfect ultrasound picture.

A Message for Expecting Parents

If your baby’s face wasn’t visible during today’s scan, don’t be discouraged.

Babies often change positions, and what wasn’t possible today may be easy at the next visit.

The most important result of an anatomy scan is not a perfect photo.

It’s the reassuring news that your baby is growing healthy and developing well.

Before long, you’ll see your baby’s face—not on an ultrasound screen, but in your arms.

Hearing that your baby is “measuring small” during an ultrasound can be stressful. Many expectant parents immediately worry that something is wrong.

However, a small baby is not always the same as IUGR (Intrauterine Growth Restriction), also known as Fetal Growth Restriction (FGR).

Understanding what IUGR means can help you feel more informed and prepared during your pregnancy.

What Is IUGR?

IUGR, or Fetal Growth Restriction (FGR), is a condition in which a baby does not grow as expected inside the uterus.

Rather than simply being naturally small, the baby may not be reaching its full growth potential because of reduced oxygen or nutrient delivery, often related to placental function.

It is important to remember that not every small baby has IUGR. Some babies are constitutionally small but completely healthy.

When Is IUGR Suspected?

Healthcare providers may suspect IUGR when an ultrasound shows:

• Estimated Fetal Weight (EFW) below the 10th percentile
• A smaller-than-expected Abdominal Circumference (AC)
• Slower growth compared with previous ultrasound examinations
• Signs suggesting reduced placental function

A diagnosis is rarely based on a single ultrasound. Instead, doctors evaluate growth over time and combine the findings with Doppler ultrasound studies.

What Causes IUGR?

Several factors may contribute to fetal growth restriction, including:

• Placental insufficiency
• High blood pressure during pregnancy
• Preeclampsia
• Multiple pregnancy (twins or more)
• Smoking or alcohol exposure
• Certain chromosomal abnormalities
• Congenital infections

In many cases, the placenta cannot deliver enough oxygen and nutrients to support normal fetal growth.

What Does the Ultrasound Evaluate?

Ultrasound assessment includes much more than the baby’s weight.

Your healthcare provider may evaluate:

• Estimated Fetal Weight (EFW)
• Abdominal Circumference (AC)
• Head Circumference (HC)
• Femur Length (FL)
• Amniotic fluid volume
• Placental appearance
• Umbilical Artery Doppler
• Middle Cerebral Artery (MCA) Doppler
• Cerebroplacental Ratio (CPR), when indicated

These measurements help determine how well the baby is growing and whether the placenta is functioning properly.

Does IUGR Mean an Early Delivery?

Not necessarily.

If Doppler studies remain normal and the baby appears healthy, many pregnancies can continue safely with close monitoring.

However, if blood flow becomes abnormal or there are signs that the baby is under stress, your healthcare team may recommend earlier delivery to improve outcomes.

Regular follow-up is one of the most important parts of managing IUGR.

Final Thoughts

Being told that your baby is small can feel overwhelming, but it does not always mean there is a serious problem.

Modern ultrasound and Doppler examinations allow healthcare providers to closely monitor fetal well-being and determine the safest time for delivery.

If you have been told your baby is measuring small, attending all scheduled prenatal appointments and discussing any concerns with your healthcare provider are the best steps you can take.