The 20-week anatomy scan, also called the mid-pregnancy ultrasound, anatomy ultrasound, or fetal anatomy scan, is one of the most detailed routine ultrasound examinations performed during pregnancy.

In the United States, a standard pregnancy ultrasound is generally performed around 18–22 weeks. The examination evaluates the baby’s growth and development and screens for many major structural abnormalities. It also assesses the placenta, amniotic fluid, fetal position, and other pregnancy-related findings.

For many parents, this is the first ultrasound where the baby’s anatomy can be examined in considerable detail—from the brain and face to the spine, heart, abdomen, kidneys, arms, and legs.

Quick Answer

The 20-week anatomy scan checks the baby’s brain, face, spine, heart, abdomen, kidneys, bladder, limbs, and other major structures. It also measures fetal growth and evaluates the placenta and amniotic fluid.

The scan can identify many important structural abnormalities, but a normal anatomy scan cannot guarantee that the baby has no health problems. Some conditions are difficult to detect before birth or may develop later in pregnancy.

What Is the 20-Week Anatomy Scan?

The anatomy scan is a detailed ultrasound examination designed to evaluate the baby’s physical development.

ACOG describes the standard ultrasound performed around 18–22 weeks as an examination that checks fetal physical development and screens for major congenital abnormalities. It can also provide information about fetal size, heart rate, position, amniotic fluid, placenta, and the number of fetuses.

The scan is sometimes called:

• 20-week ultrasound
• Anatomy scan
• Anatomy ultrasound
• Mid-pregnancy ultrasound
• Anomaly scan
• Fetal anatomy survey

Although it is commonly called the 20-week scan, it does not have to occur exactly at 20 weeks.

When Is the Anatomy Scan Done?

In the U.S., the routine anatomy ultrasound is generally performed between 18 and 22 weeks of pregnancy.

The exact timing can vary depending on the pregnancy, healthcare practice, fetal position, medical history, and whether additional imaging is required.

Sometimes a repeat examination is recommended if certain parts of the baby’s anatomy cannot be seen clearly during the first scan. Factors such as fetal position, maternal body habitus, and technical limitations can affect image quality.

What Does the 20-Week Anatomy Scan Check?

1. Baby’s Brain

The sonographer evaluates important structures of the fetal brain.

Depending on the examination, this can include assessment of:

• Lateral ventricles
• Choroid plexus
• Midline structures
• Cavum septi pellucidi
• Cerebellum
• Posterior fossa
• Cisterna magna

These views help screen for major abnormalities involving the fetal brain and central nervous system.

Also Read : 6 Week Ultrasound: What Does Your Baby Look Like at 6 Weeks?

The anatomy scan may identify findings associated with conditions such as major brain malformations or enlarged ventricles.

However, ultrasound cannot detect every neurological or developmental condition.

2. Face

The fetal face is also evaluated.

The sonographer may examine:

• Facial profile
• Upper lip
• Nose and surrounding structures
• Orbits when indicated
• Facial symmetry

One reason the face is carefully evaluated is to screen for structural abnormalities such as cleft lip.

Some facial abnormalities are easier to identify than others, and fetal position can affect visualization.

3. Spine

The spine is examined along its length to evaluate the vertebral column and surrounding tissues.

The sonographer looks at the spine in different ultrasound planes and evaluates the relationship between the spine and overlying skin.

The examination can detect many major spinal abnormalities, including open spina bifida.

The standard ultrasound examination includes assessment of the fetal spine as part of the anatomy survey.

4. Heart

The fetal heart is one of the most important parts of the anatomy scan.

Routine cardiac screening generally includes evaluation of:

• Four-chamber view
• Heart position
• Heart size
• Left ventricular outflow tract
• Right ventricular outflow tract
• Three-vessel view
• Three-vessel-trachea view when technically feasible

The scan may identify signs suggesting a congenital heart abnormality.

However, some fetal heart defects are difficult to detect on a routine anatomy scan. If the cardiac views are abnormal or incomplete, or if the pregnancy has specific risk factors, the provider may recommend a fetal echocardiogram.

A fetal echocardiogram is a more detailed examination specifically focused on the baby’s heart.

5. Abdomen

The fetal abdomen is examined for the presence, position, and appearance of important structures.

The sonographer may evaluate:

• Stomach
• Abdominal wall
• Umbilical cord insertion
• Bowel
• Liver region
• Abdominal organs

The stomach should generally be visible because the fetus swallows amniotic fluid.

The abdominal wall is also examined for abnormalities such as omphalocele or gastroschisis.

6. Kidneys and Bladder

The anatomy scan checks the fetal urinary system.

The sonographer evaluates:

• Both kidneys
• Renal appearance
• Bladder
• Urinary tract-related findings

The fetal bladder is normally visible because the baby’s kidneys produce urine, which contributes to amniotic fluid.

Major abnormalities involving the kidneys or urinary tract may sometimes be detected during the anatomy scan.

7. Arms and Legs

The sonographer examines the fetal limbs, including:

• Upper arms
• Forearms
• Hands
• Thighs
• Lower legs
• Feet

The long bones may be measured as part of fetal biometry.

The scan can identify some major skeletal abnormalities, although it cannot evaluate every detail of the baby’s fingers and toes or predict all future developmental problems.

8. Growth and Measurements

The anatomy scan also includes fetal measurements.

Also Read : 10 Early Pregnancy Symptoms Most Women Miss

Common biometric measurements include:

• Biparietal diameter (BPD)
• Head circumference (HC)
• Abdominal circumference (AC)
• Femur length (FL)

These measurements help assess fetal size and growth and may be used to calculate an estimated fetal weight. The AIUM’s obstetric ultrasound parameters include these measurements as part of standard fetal assessment.

The measurements are interpreted according to gestational age and appropriate reference standards.

A baby’s measurement being slightly ahead or behind does not automatically mean there is a problem.

9. Placenta and Amniotic Fluid

The anatomy scan also evaluates structures around the baby.

Placenta

The sonographer documents the placenta’s:

• Location
• Relationship to the cervix
• Appearance when relevant

A low-lying placenta or placenta previa may require follow-up later in pregnancy depending on the findings.

Amniotic Fluid

The amount of amniotic fluid is also assessed.

Too much or too little fluid can sometimes be associated with maternal or fetal conditions and may require additional evaluation.

ACOG lists placental location and amniotic fluid among the information that can be obtained during a standard pregnancy ultrasound.

What About the Umbilical Cord?

The sonographer may also evaluate the umbilical cord, including its insertion and, when appropriate, the number of vessels.

Cord abnormalities can sometimes be associated with other fetal or pregnancy findings and may influence whether additional monitoring is recommended.

For pregnancies requiring a detailed anatomy examination, professional guidelines include assessment of the placenta and umbilical cord anatomy.

Can the Anatomy Scan Detect Birth Defects?

Yes. The anatomy scan can detect many major structural abnormalities, but it cannot detect every possible condition.

ACOG states that ultrasound can detect many congenital anomalies, while screening guidelines emphasize that a normal scan does not rule out all birth defects or health conditions.

The ability to detect a particular abnormality depends on factors such as:

• Type of condition
• Gestational age
• Fetal position
• Image quality
• Maternal body habitus
• Ultrasound equipment
• Experience of the sonographer and interpreting clinician

For example, some major structural abnormalities are relatively easy to visualize, while certain heart defects can be more difficult to identify.

Therefore, “normal anatomy scan” means no abnormality was identified on that examination—not that every possible condition has been ruled out.

What Happens During the Scan?

Most anatomy scans are performed as a transabdominal ultrasound.

You typically lie on an examination bed while ultrasound gel is applied to your abdomen. The sonographer moves the transducer across the abdomen to obtain images.

The examination may take longer than a routine ultrasound because many different anatomical views are required.

Sometimes the baby is facing an unfavorable direction, making certain structures difficult to see. You may be asked to change position or walk around and return for additional images.

If important anatomy cannot be adequately visualized, a repeat ultrasound may be recommended. AIUM guidance specifically recognizes that fetal position and other technical factors can limit visualization and that follow-up imaging may be helpful.

What If Something Abnormal Is Found?

An abnormal or incomplete finding does not automatically mean that the baby has a serious condition.

Your healthcare provider may recommend:

• Repeat ultrasound
• Detailed fetal anatomy ultrasound
• Fetal echocardiogram
• Maternal-fetal medicine consultation
• Genetic counseling
• Additional prenatal testing
• Follow-up imaging later in pregnancy

The next step depends on the specific finding.

For example, an isolated soft ultrasound marker may be managed differently from a suspected structural heart defect.

A detailed fetal anatomic ultrasound may be appropriate when a standard examination identifies or raises suspicion for an abnormality.

When to Seek Medical Care

The anatomy scan itself is a routine prenatal examination, but contact your pregnancy care provider if:

• Your report mentions a suspected fetal abnormality.
• The scan could not adequately visualize an important structure.
• Your provider recommends additional testing.
• You have questions about an abnormal ultrasound finding.
• You experience pregnancy symptoms such as heavy bleeding, severe abdominal pain, fluid leakage, or significantly decreased fetal movement.

An ultrasound report should be interpreted in the context of the entire pregnancy rather than by looking at one measurement or finding alone.