Anatomy Scan In Pregnancy: Purpose, Timing, Normal Measurements, And What It Detects

If your doctor has advised an anatomy scan, it is natural to feel both excited and anxious. This scan is an important part of pregnancy care and gives your doctor a detailed look at your baby’s development around the middle of pregnancy.

An anatomy scan, also called a usg anomaly scan or fetal anomaly scan, helps check your baby’s organs, body structure, placenta, amniotic fluid, and overall fetal growth. In most pregnancies, the scan is reassuring. If something needs a closer look, it helps your doctor plan the next steps early and carefully.

What Is An Anatomy Scan?

If you are wondering what is anomaly scan, it is a detailed pregnancy ultrasound usually done in the second trimester. It is often called the 20-week ultrasound because it is commonly performed around that stage of pregnancy.

This scan is also known as a Level 2 Ultrasound. It is more detailed than an early pregnancy scan because, by this time, your baby has grown enough for important structures to be examined more clearly.

During the anatomy scan, the sonographer looks at your baby’s head, face, brain, heart, spine, stomach, kidneys, bladder, arms, legs, hands, and feet. The scan also checks the placenta, amniotic fluid, heartbeat, and key measurements linked to fetal growth.

Why Is The 20-Week Anatomy Scan Important?

The anatomy scan is an important mid-pregnancy check because it helps your doctor understand how your baby is developing.

It can help:

• Check your baby’s organs and body structure
• Assess fetal growth using standard measurements
• Review the placenta’s position
• Check the amount of amniotic fluid
• Record the baby’s heartbeat and rhythm
• Identify some structural concerns that may need follow-up

This scan does not diagnose every condition. However, it is a very useful screening test and helps your doctor monitor the pregnancy more confidently.

Purpose Of The 20-Week Ultrasound

The purpose of the 20-week ultrasound is to give a detailed view of your baby and the pregnancy.

It is usually done to:

• Examine the baby’s brain, heart, spine, face, stomach, kidneys, bladder, limbs, hands, and feet
• Check fetal growth with measurements such as head size, belly size, and leg bone length
• Review Fetal Biometry to see if growth matches the stage of pregnancy
• Check the placenta’s location
• Assess the amount of amniotic fluid
• Record the fetal heart rate
• Examine the umbilical cord and its attachment
• Look for signs of selected structural abnormalities
• Offer a clearer picture of how the pregnancy is progressing

When To Get An Anatomy Scan In Pregnancy

The anatomy scan is usually done between 18 and 22 weeks of pregnancy.

Here is why this timing matters:

1. Your Baby Is Developed Enough For Detailed Imaging
   By this stage, the organs and body parts are formed enough to be checked properly.
2. It Helps Assess Growth At The Right Time
   Important 20 week ultrasound measurements can be compared with your gestational age.
3. It Allows Time For Follow-Up If Needed
   If anything is unclear, your doctor may suggest another scan or specialist review.
4. It Fits The Usual Anomaly Scan Week Window
   The common anomaly scan week range is around 18 to 22 weeks, though the exact timing can vary slightly.

What Does The 20-Week Ultrasound Detect?

The 20-week ultrasound looks at many important areas of your baby’s body and the pregnancy.

It may detect or assess:

• Brain and skull development
• Facial structures such as the lips and nose
• Heart structure and heartbeat
• Spine formation
• Stomach and abdominal wall
• Kidneys and bladder
• Arms, legs, hands, fingers, feet, and toes
• Placenta position
• Amniotic fluid level
• Umbilical cord attachment
• Overall fetal growth and size for gestational age

The scan may help identify some structural concerns such as certain heart defects, spine problems, abdominal wall defects, kidney-related concerns, or cleft lip. However, it cannot detect all conditions.

Understanding The Fetal Anatomy Scan Report

A fetal anatomy scan report usually includes observations about your baby’s body structure, heartbeat, placenta, amniotic fluid, and growth measurements.

Your fetal anatomy scan report may mention:

• Fetal heart activity
• Placenta location
• Amniotic fluid status
• Fetal Biometry measurements
• Organ views that were seen clearly
• Whether the anatomy appears normal for the stage of pregnancy
• Whether any follow-up scan is needed

It is important to remember that this is a screening report. It helps identify whether anything looks normal, unclear, or needs further assessment. It does not always give a final diagnosis.

Anomaly Scan Week And Its Significance

The anomaly scan week is important because it is the best time to see key body structures in enough detail.

If the scan is done too early, some structures may not be visible clearly. If it is done during the usual 18 to 22 week window, the sonographer can assess the baby more thoroughly while there is still time to plan any additional care if needed.

This is why the fetal anomaly scan is considered a routine and valuable part of antenatal care.

Anomaly Scan Normal Measurements

When people search for anomaly scan normal measurements, they usually want to know whether the baby’s size matches the stage of pregnancy.

Some common measurements include:

• Biparietal Diameter: Measures the width of the baby’s head
• Head Circumference: Measures the distance around the head
• Abdominal Circumference: Measures the distance around the baby’s abdomen
• Femur Length: Measures the length of the thigh bone
• Fetal Biometry: A group of standard measurements used to assess fetal growth

These values are interpreted together, not alone. A single measurement does not always mean there is a problem. Your doctor looks at the full picture, including gestational age and overall fetal growth.

20-Week Ultrasound Measurements: What Doctors Check

The 20 week ultrasound measurements help doctors understand whether your baby is growing as expected.

These measurements commonly include:

• Biparietal Diameter
• Head Circumference
• Abdominal Circumference
• Femur Length
• Fetal Biometry as an overall growth assessment

Biparietal Diameter helps estimate head size. Abdominal Circumference is useful for assessing body size and fetal growth. Fetal Biometry combines these values to give a broader picture of development.

Doctors do not rely on only one number. They review all 20 week ultrasound measurements together to understand whether growth appears appropriate for your stage of pregnancy.

What To Expect During The 20-Week Ultrasound

Knowing what happens during the scan can help you feel more prepared.

1. You Will Lie Down On The Examination Couch
   The scan is usually done over your abdomen.
2. Gel Will Be Applied To Your Tummy
   This helps the probe move smoothly and improves image quality.
3. The Sonographer Will Move The Probe Over Your Abdomen
   This creates images of your baby on the screen.
4. The Sonographer Will Take Pictures And Measurements
   They will examine body parts and record Fetal Biometry values.
5. You May Be Asked To Change Position
   If the baby is not in a good position, you may be asked to move, walk a little, or return after a short break.
6. The Scan Usually Takes 30 To 45 Minutes
   In some cases, it may take longer if more views are needed.
7. Your Doctor Will Discuss The Results
   The sonographer may stay quiet while doing the scan. This is normal. The final interpretation usually comes from your doctor.

What Happens After The 20-Week Ultrasound?

After the scan, one of the following may happen:

• Your doctor may review the results on the same day
• You may get the report at a follow-up visit
• You may be told that everything looks normal and reassuring
• You may be advised to repeat the scan if some views were incomplete
• You may be referred for more tests if anything needs closer assessment

In most pregnancies, the anatomy scan is a positive and reassuring milestone.

How To Prepare For The Scan

There is usually not much preparation needed for an anatomy scan.

You may be advised to:

• Wear comfortable clothing
• Reach the centre a little early
• Carry previous pregnancy records if needed
• Ask in advance whether a full bladder is required
• Avoid worry if the scan takes longer than expected

Are There Any Risks Associated With The 20-Week Ultrasound?

The 20-week ultrasound is generally considered safe. It uses sound waves, not radiation.

It is a non-invasive scan and does not harm your baby when used as part of standard pregnancy care. The main difficulty is usually emotional rather than physical. If the images are unclear or if something unexpected is seen, you may feel worried. In such cases, your doctor will guide you on what it means and what to do next.

How Accurate Is The 20-Week Ultrasound?

The anatomy scan is a very useful screening test, but it is not perfect.

It can detect many structural concerns, but not all of them. Accuracy can be affected by:

• The baby’s position
• The stage of pregnancy
• Maternal body build
• Image quality
• Whether all parts could be seen clearly on that day

Most scans are reassuring. If some parts are not seen well, your doctor may advise a repeat scan rather than assuming there is a problem.

Can The 20-Week Ultrasound Detect Gender?

The scan may show the baby’s sex if the baby is in a position that allows a clear view.

A few points are worth keeping in mind:

• It depends on the baby’s position
• Not every scan gives a clear view
• Some parents prefer not to know
• What can be shared may depend on local regulations and clinic policy

What If The Scan Shows A Potential Abnormality?

If the scan shows a possible concern, it does not always mean there is definitely a serious problem.

Sometimes the issue is simply that the baby’s position prevented a clear view. In other cases, your doctor may advise:

• A repeat ultrasound
• A specialist scan
• Fetal echocardiography to look more closely at the heart
• Genetic counselling
• Diagnostic tests if medically appropriate

Your doctor will explain the finding carefully and guide you through the next steps. Early information can help your healthcare team plan the best possible care for you and your baby.

Limitations Of The Anatomy Scan

The anatomy scan is detailed, but it has limits.

It cannot:

• Detect every birth defect or health condition
• Guarantee that the baby has no medical problems
• Predict all issues that may appear later in pregnancy or after birth
• Always give clear views if the baby’s position is difficult

This is why the anatomy scan is best understood as an important screening tool, not a complete guarantee.

Frequently Asked Questions

What Measurements Are Taken During The 20-Week Ultrasound?

Common 20 week ultrasound measurements include:

• Biparietal Diameter
• Head Circumference
• Abdominal Circumference
• Femur Length
• Fetal Biometry overall assessment

These measurements help your doctor assess size, growth pattern, and fetal growth in relation to your gestational age.

What Happens If An Anomaly Is Found In The 20-Week Ultrasound?

If a possible anomaly is seen, your doctor may advise a repeat scan, specialist review, or additional tests. This helps confirm whether there is a real concern and what care may be needed next.

How Long Does A 20-Week Ultrasound Take?

A 20-week ultrasound usually takes around 30 to 45 minutes. It may take longer if the baby is moving a lot or is not in a position that allows clear images.

Is The 20-Week Ultrasound Safe For My Baby?

Yes. The scan is generally considered safe because it uses sound waves rather than radiation. It is a standard part of pregnancy care.

When Should The Anatomy Scan Be Done?

The anatomy scan is usually done between 18 and 22 weeks of pregnancy. This is the ideal time for checking organ development and growth in detail.

Can I Find Out The Baby’s Sex During The Anatomy Scan?

The scan may be able to show the baby’s sex if the position allows it. However, whether this information is shared can depend on local rules and the centre’s policy.

What Happens If The Anatomy Scan Shows A Potential Abnormality?

Your doctor may recommend further scans or tests to get more clarity. You may also be referred to a specialist. This helps your care team understand the finding and plan support early.

Is A USG Anomaly Scan Different From A Regular Pregnancy Ultrasound?

Yes. A usg anomaly scan is more detailed than an early pregnancy ultrasound. It is designed to examine the baby’s structure, important organs, placenta, and growth measurements in greater detail.

The Bottom Line

The anatomy scan is an important mid-pregnancy ultrasound that helps check your baby’s body structure, placenta, amniotic fluid, and fetal growth. It is usually done between 18 and 22 weeks and gives useful information about how the pregnancy is progressing.

Most anatomy scans are reassuring. If any finding needs more attention, the scan gives your doctor a chance to guide you early and plan the next steps with care.

At Metropolis Healthcare, timely and dependable diagnostics can support you at every stage of your health journey. With advanced technology, reliable reporting, and a patient-focused approach, Metropolis Healthcare helps make important health checks more accessible and reassuring for you and your family.

References

1. American College of Obstetricians and Gynecologists. Ultrasound Exams.
2. NHS. 20-Week Screening Scan.
3. International Society of Ultrasound in Obstetrics and Gynecology. Practice Guidelines For Performance Of The Routine Mid-Trimester Fetal Ultrasound Scan.
4. Salomon LJ, Alfirevic Z, Berghella V, et al. Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2022.