Part 2: Anomaly Scan (20-Week Pregnancy Scan): A Complete Guide to Fetal Anatomy Ultrasound

What is an Anomaly Scan?

An Anomaly Scan is one of the most important ultrasound examinations performed during pregnancy. It is a detailed fetal anatomy ultrasound designed to evaluate whether the developing baby’s organs and body structures are forming normally.

This examination is commonly performed between 18 and 22 weeks of pregnancy, when most fetal organs are sufficiently developed for detailed assessment. Because of this timing, it is also known as the 20-week pregnancy scan, Mid-Pregnancy Scan, Level II Ultrasound, or Targeted Fetal Anatomy Scan.

Unlike a routine pregnancy ultrasound that mainly confirms fetal growth, heartbeat, and gestational age, an Anomaly Scan provides a comprehensive anatomical evaluation of the fetus. The sonographer systematically examines the baby’s brain, face, spine, heart, lungs, stomach, kidneys, bladder, limbs, placenta, umbilical cord, and amniotic fluid.

The primary goal is to identify structural abnormalities that may affect fetal development and to support appropriate prenatal care planning. Early identification of certain conditions allows obstetricians, fetal medicine specialists, and parents to make informed decisions regarding pregnancy management and delivery planning.

What is an Anomaly Scan?
What Does the Word “Anomaly” Mean?
Why is an Anomaly Scan Important?
When Should an Anomaly Scan Be Performed?
Who Should Have an Anomaly Scan?
What Does an Anomaly Scan Evaluate?
Fetal Anatomy Assessment
Fetal Biometry Measurements
Placenta Assessment
Amniotic Fluid Assessment
Umbilical Cord Assessment
Congenital Abnormalities That Can Be Detected
Can Every Birth Defect Be Diagnosed?
Is a 2D Convex Probe Enough?
The Role of 3D and 4D Ultrasound
Color Doppler During Anomaly Scan
Patient Preparation
How Long Does the Scan Take?
What Happens If an Abnormality Is Found?
Advantages of an Anomaly Scan
Limitations of the Examination
Frequently Asked Questions
Conclusion

What is an Anomaly Scan?

What Does the Word “Anomaly” Mean?

The word “Anomaly” means an abnormality, deviation from normal development, or structural difference.

In obstetrics, a fetal anomaly refers to a congenital structural abnormality that develops before birth. These abnormalities may involve a single organ, multiple organs, or an entire body system.

Examples include:

Neural tube defects
Cleft lip and palate
Congenital heart defects
Kidney abnormalities
Limb deformities
Abdominal wall defects
Skeletal abnormalities

It is important to understand that not every anomaly is life-threatening. Some conditions are mild and treatable after birth, while others may require specialized prenatal monitoring or neonatal care.

Why is an Anomaly Scan Important?

An Anomaly Scan is considered one of the most valuable prenatal ultrasound examinations because it provides a detailed assessment of fetal anatomy rather than simply confirming the baby’s presence or heartbeat.

The scan helps healthcare professionals:

Evaluate normal fetal development
Detect many congenital structural abnormalities
Assess fetal growth
Examine the placenta
Measure amniotic fluid
Assess the umbilical cord
Plan further investigations when required
Improve pregnancy management
Prepare parents for appropriate neonatal care if necessary

For most pregnancies, the scan provides reassurance that fetal development appears normal. When an abnormality is suspected, early diagnosis allows timely referral to fetal medicine specialists and appropriate follow-up investigations.

When Should an Anomaly Scan Be Performed?

International obstetric guidelines recommend performing the examination between 18 and 22 weeks of gestation.

At this stage:

The fetal organs have developed sufficiently.
The baby is large enough for detailed anatomical evaluation.
Ultrasound visualization is generally optimal.
Most major congenital structural abnormalities can be assessed.

If visualization is limited because of fetal position, maternal body habitus, or other technical factors, a repeat examination may be recommended.

Who Should Have an Anomaly Scan?

An Anomaly Scan is recommended for all pregnant women, regardless of age or pregnancy risk.

However, it is particularly important for pregnancies with:

Previous baby with congenital abnormalities
Maternal diabetes
Family history of genetic disorders
Abnormal first-trimester screening results
Increased maternal age
Multiple pregnancy (twins or more)
Suspected fetal growth abnormalities
Previous abnormal ultrasound findings

Even in low-risk pregnancies, this examination remains an essential component of routine prenatal care because many congenital abnormalities occur without known risk factors.

What Does an Anomaly Scan Evaluate?

An Anomaly Scan is a systematic examination of the fetus from head to toe. During the scan, the sonographer follows a structured protocol to assess every major organ and body system. The objective is to confirm that fetal development is progressing normally and to identify any structural abnormalities that may require further investigation.

A complete fetal anatomy scan generally evaluates the following areas:

Head and Brain
Face and Neck
Spine
Chest and Lungs
Heart
Abdomen
Gastrointestinal Tract
Kidneys and Urinary Bladder
Upper and Lower Limbs
Placenta
Amniotic Fluid
Umbilical Cord
Fetal Growth Measurements

Complete Fetal Anatomy Assessment

1. Head and Brain Assessment

The fetal brain is one of the most important structures examined during the Anomaly Scan.

The sonographer evaluates:

Skull shape and integrity
Biparietal Diameter (BPD)
Head Circumference (HC)
Brain hemispheres
Falx cerebri
Lateral ventricles
Choroid plexus
Cavum Septi Pellucidi (CSP)
Thalami
Cerebellum
Cisterna Magna
Posterior fossa

This assessment helps identify conditions such as:

Hydrocephalus
Anencephaly
Ventriculomegaly
Neural tube defects
Dandy-Walker spectrum
Other brain malformations

2. Face Assessment

The baby’s face is examined in multiple ultrasound planes.

Structures evaluated include:

Forehead
Orbits (Eyes)
Nose
Nasal Bone
Lips
Upper Lip
Chin
Facial Profile

The examination may detect:

Cleft Lip
Facial asymmetry
Micrognathia
Certain craniofacial abnormalities

3. Neck Assessment

The neck region is evaluated for:

Normal alignment
Masses
Cystic lesions
Neck thickness (when clinically indicated)

4. Spine Assessment

The fetal spine is examined from the neck to the lower back.

The sonographer assesses:

Cervical Spine
Thoracic Spine
Lumbar Spine
Sacral Spine
Skin covering
Vertebral alignment

This helps detect:

Spina Bifida
Hemivertebra
Kyphosis
Scoliosis
Open neural tube defects

5. Heart Assessment

The fetal heart is one of the most detailed parts of the examination.

Evaluation includes:

Cardiac position
Heart rate
Cardiac rhythm
Four-Chamber View
Right ventricular outflow tract (RVOT)
Left ventricular outflow tract (LVOT)
Three Vessel View (when possible)

The scan may identify many congenital heart defects, although not every heart condition can be detected before birth.

6. Chest Assessment

The chest examination includes:

Lung appearance
Diaphragm
Heart position
Thoracic symmetry

Possible abnormalities include:

Congenital diaphragmatic hernia
Lung lesions
Thoracic masses

7. Abdomen Assessment

The abdominal examination evaluates:

Stomach
Liver
Bowel
Abdominal wall
Liver position

Possible abnormalities include:

Gastroschisis
Omphalocele
Bowel obstruction
Abdominal wall defects

8. Kidneys and Urinary System

The urinary tract is carefully assessed.

Structures include:

Right kidney
Left kidney
Renal pelvis
Urinary bladder
Ureters (when visible)

Possible abnormalities include:

Hydronephrosis
Renal agenesis
Multicystic kidneys
Bladder abnormalities

9. Upper Limbs Assessment

The sonographer evaluates:

Humerus
Radius
Ulna
Hands
Fingers

Assessment includes:

Bone length
Bone shape
Movement
Symmetry

10. Lower Limbs Assessment

The lower extremities include:

Femur
Tibia
Fibula
Feet
Toes

The examination helps identify:

Clubfoot
Limb shortening
Skeletal abnormalities

Fetal Biometry Measurements

Accurate fetal measurements are an essential part of every Anomaly Scan.

Common measurements include:

Biparietal Diameter (BPD)

Measures the width of the baby’s head.

Head Circumference (HC)

Evaluates overall head growth.

Abdominal Circumference (AC)

Measures fetal abdominal growth.

Femur Length (FL)

Measures the length of the thigh bone.

These measurements help:

Confirm gestational age
Assess fetal growth
Detect growth restriction
Identify unusually large fetal size

Placenta Assessment

The placenta is carefully examined to evaluate:

Placental location
Placental thickness
Placental appearance
Distance from the cervix (when necessary)

This helps identify conditions such as:

Low-lying placenta
Placenta previa
Placental abnormalities

Amniotic Fluid Assessment

The amount of amniotic fluid is evaluated because it reflects fetal well-being.

Too little fluid (Oligohydramnios) or too much fluid (Polyhydramnios) may require additional monitoring and clinical assessment.

Umbilical Cord Assessment

The umbilical cord is examined for:

Cord insertion
Number of vessels
General appearance

A normal umbilical cord typically contains:

Two umbilical arteries
One umbilical vein

Assessment of the cord contributes to the overall evaluation of fetal development and pregnancy health.

Congenital Abnormalities That Can Be Detected

An Anomaly Scan is designed to identify many structural abnormalities that develop before birth. Although no ultrasound examination can detect every condition, a detailed fetal anatomy scan can identify a significant number of congenital anomalies.

Some of the abnormalities that may be detected include:

Brain and Central Nervous System

Anencephaly
Hydrocephalus
Ventriculomegaly
Holoprosencephaly
Dandy-Walker malformation
Neural tube defects

Face

Cleft lip
Facial clefts
Micrognathia
Abnormal facial profile

Spine

Spina bifida
Open spinal defects
Vertebral abnormalities

Heart

Four-chamber abnormalities
Major congenital heart defects
Abnormal great vessels
Cardiac position abnormalities

Chest

Congenital diaphragmatic hernia
Lung malformations
Thoracic masses

Abdomen

Gastroschisis
Omphalocele
Bowel obstruction
Abdominal wall defects

Kidneys and Urinary System

Hydronephrosis
Renal agenesis
Multicystic dysplastic kidney
Enlarged bladder

Limbs

Clubfoot
Missing limbs
Limb shortening
Skeletal dysplasia

Can Every Birth Defect Be Diagnosed?

The answer is No.

Even with modern ultrasound technology and experienced sonographers, no Anomaly Scan can detect 100% of congenital abnormalities.

Several factors influence detection:

Gestational age
Fetal position
Maternal body habitus
Amount of amniotic fluid
Ultrasound equipment quality
Sonographer’s experience
Type of abnormality

Some conditions become visible only later in pregnancy, while others are too subtle to identify during routine screening.

Therefore, a normal Anomaly Scan significantly reduces the likelihood of major structural abnormalities but does not completely eliminate all risks.

Is a 2D Convex Probe Enough for an Anomaly Scan?

Yes.

A high-quality 2D Convex Probe is the standard and most important tool for performing a routine fetal Anomaly Scan.

Most international obstetric ultrasound guidelines are based primarily on detailed 2D ultrasound imaging.

A quality 2D system allows evaluation of:

Brain
Spine
Heart
Abdomen
Kidneys
Bladder
Limbs
Placenta
Amniotic fluid
Fetal growth

Therefore, the diagnostic accuracy of an Anomaly Scan depends far more on:

Image quality
Machine performance
Proper ultrasound settings
Sonographer experience

than simply having 3D or 4D capability.

Role of 3D and 4D Ultrasound

Although 3D and 4D ultrasound provide impressive images, they are considered complementary imaging techniques rather than replacements for standard 2D ultrasound.

3D Ultrasound may help evaluate:

Cleft lip
Facial abnormalities
Limb deformities
Skeletal abnormalities
Surface anatomy

4D Ultrasound provides:

Real-time three-dimensional imaging
Observation of fetal movement
Facial expressions
Limb movement
Improved parental visualization

However, 3D/4D ultrasound is not mandatory for routine Anomaly Scan, and many normal pregnancies are assessed completely using high-quality 2D imaging.

Role of Color Doppler

Color Doppler is sometimes used during an Anomaly Scan when additional vascular assessment is clinically indicated.

It may assist in evaluating:

Cardiac blood flow
Umbilical cord vessels
Placental circulation
Selected fetal vessels

Color Doppler is used selectively and is not required in every routine examination.

Patient Preparation Before the Scan

Most pregnant women do not require any special preparation before an Anomaly Scan.

General recommendations include:

Wear comfortable clothing.
Bring previous ultrasound reports if available.
Carry antenatal records.
Arrive on time for the appointment.
Follow your healthcare provider’s instructions.

A moderately filled bladder may occasionally be requested in early pregnancy, but in most second-trimester scans, this is not necessary.

What Happens If an Abnormality Is Found?

If a structural abnormality is suspected, the healthcare provider may recommend further evaluation depending on the clinical findings.

Additional investigations may include:

Repeat detailed ultrasound
Fetal Echocardiography
Genetic counseling
Diagnostic genetic testing (when clinically indicated)
Maternal-Fetal Medicine consultation
Serial follow-up scans

The next steps depend on the type and severity of the suspected condition.

Advantages of an Anomaly Scan

An Anomaly Scan provides several important clinical benefits:

Early detection of many congenital abnormalities
Assessment of fetal growth
Evaluation of placental location
Measurement of amniotic fluid
Identification of multiple pregnancies
Better pregnancy management
Improved delivery planning
Appropriate referral to specialists when needed
Reassurance when fetal anatomy appears normal

Limitations of an Anomaly Scan

Despite advances in ultrasound technology, every examination has limitations.

These include:

Not all birth defects can be detected.
Fetal position may limit visualization.
Maternal obesity can reduce image quality.
Low amniotic fluid may affect assessment.
Some abnormalities develop later in pregnancy.
Very small defects may not be visible.
Ultrasound cannot diagnose every genetic disorder.

For these reasons, ultrasound findings are always interpreted alongside clinical history, laboratory tests, and other prenatal assessments when appropriate.

References

For medical accuracy, base your content on internationally recognized professional guidance, including:

International Society of Ultrasound in Obstetrics and Gynecology (ISUOG)
Fetal Medicine Foundation (FMF)
American College of Obstetricians and Gynecologists (ACOG)
World Health Organization (WHO) guidance where applicable

Bangladesh Context: Anomaly Scan Services and Ultrasound Technology

Anomaly Scan in Bangladesh

In Bangladesh, an Anomaly Scan has become an essential part of routine antenatal care for pregnant women. Most obstetricians and gynecologists recommend a detailed fetal anatomy ultrasound between 18 and 22 weeks of pregnancy to evaluate fetal development and detect possible congenital structural abnormalities.

Today, many hospitals, maternity clinics, and diagnostic centers across Dhaka, Chattogram, Khulna, Rajshahi, Sylhet, Barishal, Rangpur, and Mymensingh offer anomaly scan services using modern ultrasound systems.

The quality of an Anomaly Scan depends on several factors, including:

High-resolution ultrasound machine
Premium 2D Convex Probe
Experienced sonologist or radiologist
Proper scanning protocol
Regular machine calibration and maintenance

Choosing the Right Ultrasound Machine for Anomaly Scan

For accurate fetal anatomy assessment, image quality is more important than simply having 3D or 4D capability.

Healthcare providers should consider:

Excellent 2D image resolution
High frame rate
Advanced tissue optimization
Reliable convex probe performance
Color Doppler capability
Regular software updates
Professional after-sales service

Why Image Quality Matters

A detailed fetal anatomy scan relies on clear visualization of:

Brain
Heart
Spine
Face
Kidneys
Placenta
Limbs
Umbilical cord

Poor image quality may reduce diagnostic confidence and make certain anatomical structures difficult to assess.

Refurbished Ultrasound Machines for Bangladesh

Many hospitals and diagnostic centers in Bangladesh successfully use refurbished premium ultrasound systems from globally recognized manufacturers.

When purchasing a refurbished ultrasound machine, buyers should verify:

Original manufacturer
Year of manufacture
Probe compatibility
Software version
Service history
Preventive maintenance records
Warranty
Installation and application training
Availability of spare parts

Why Choose UltraTech BD?

UltraTech BD supplies high-quality refurbished and pre-owned ultrasound systems for hospitals, diagnostic centers, and healthcare providers throughout Bangladesh.

Services include:

Professional equipment consultation
Ultrasound machine installation
Application training
Preventive maintenance
Probe testing
Repair services
Spare parts support
After-sales technical assistance

Choosing the right ultrasound equipment with reliable technical support helps healthcare professionals deliver more accurate diagnoses and improve patient care.

Frequently Asked Questions (FAQs)

1. What is an Anomaly Scan?

An Anomaly Scan is a detailed ultrasound examination performed during pregnancy to assess the baby’s anatomy and identify possible structural abnormalities. It is commonly performed between 18 and 22 weeks of gestation.

2. When is the best time to have an Anomaly Scan?

The recommended time is between 18 and 22 weeks of pregnancy, when most fetal organs are sufficiently developed for detailed evaluation.

3. Is an Anomaly Scan mandatory?

Although it is not legally mandatory, it is strongly recommended as part of routine prenatal care because it helps assess fetal development and detect many congenital abnormalities.

4. Is an Anomaly Scan safe?

Yes. Diagnostic ultrasound is considered safe during pregnancy when performed by trained healthcare professionals using appropriate clinical guidelines.

5. How long does the examination take?

Most scans take 30–45 minutes, although the duration may vary depending on fetal position, maternal body habitus, and whether additional images are required.

6. Does the scan hurt?

No. It is a painless and non-invasive examination performed over the mother’s abdomen using ultrasound gel and a transducer.

7. Can an Anomaly Scan detect every birth defect?

No. While many structural abnormalities can be detected, no ultrasound examination can identify 100% of congenital conditions.

8. Is a 2D Convex Probe sufficient?

Yes. A high-quality 2D Convex Probe remains the standard imaging tool for routine fetal anatomy assessment and is used in most anomaly scans worldwide.

9. Is 4D Ultrasound necessary?

No. 3D and 4D ultrasound may provide additional visualization of selected fetal structures but are not mandatory for routine anomaly screening.

10. Can Color Doppler be used during an Anomaly Scan?

Yes. Color Doppler may be used when additional assessment of blood flow, the fetal heart, or the umbilical cord is clinically indicated.

11. What organs are examined during an Anomaly Scan?

The scan evaluates the brain, face, spine, heart, lungs, stomach, kidneys, bladder, limbs, placenta, umbilical cord, and amniotic fluid.

12. Can the baby’s gender be identified?

In many cases, fetal sex can be identified if the baby’s position allows and if disclosure is permitted under local regulations and requested by the parents.

13. What happens if an abnormality is suspected?

Your healthcare provider may recommend additional imaging, fetal echocardiography, genetic counseling, or referral to a maternal-fetal medicine specialist.

14. Can obesity affect the quality of the scan?

Yes. Increased maternal body mass index (BMI) may reduce image quality and make some anatomical structures more difficult to visualize.

15. Is fasting required before the scan?

No. Fasting is generally not required unless specifically advised by your healthcare provider.

16. Can twins have an Anomaly Scan?

Yes. Twin and multiple pregnancies also require a detailed fetal anatomy assessment, although the examination may take longer.

17. What if the baby is not in a suitable position?

If visualization is limited, your healthcare provider may recommend changing position, walking for a short time, or scheduling a repeat scan.

18. Is an Anomaly Scan the same as a routine pregnancy ultrasound?

No. A routine ultrasound confirms fetal growth and viability, while an Anomaly Scan provides a much more detailed evaluation of fetal anatomy.

19. Can an Anomaly Scan diagnose genetic disorders?

Ultrasound may detect physical findings associated with certain genetic conditions, but it cannot diagnose all chromosomal or genetic disorders. Additional tests may be required.

20. Why is an Anomaly Scan important?

It provides a detailed assessment of fetal anatomy, supports early detection of many structural abnormalities, and helps healthcare providers plan appropriate prenatal care and delivery management.

Conclusion

An Anomaly Scan is one of the most valuable ultrasound examinations performed during pregnancy. It offers a comprehensive assessment of fetal anatomy, allowing healthcare professionals to evaluate the development of major organs, monitor fetal growth, assess the placenta and amniotic fluid, and identify many structural abnormalities before birth.

The examination is typically performed between 18 and 22 weeks of gestation, when fetal anatomy can be assessed in greatest detail. A systematic evaluation of the brain, face, spine, heart, chest, abdomen, kidneys, bladder, limbs, placenta, and umbilical cord provides important clinical information that supports safe prenatal care.

Although modern ultrasound technology has significantly improved the detection of congenital abnormalities, no examination can identify every condition. The accuracy of an Anomaly Scan depends on several factors, including fetal position, gestational age, image quality, ultrasound equipment, and the expertise of the sonographer. For this reason, ultrasound findings should always be interpreted in the context of the patient’s clinical history and other prenatal investigations.

Routine fetal anatomy assessment is primarily performed using a high-quality 2D Convex Ultrasound Probe. While 3D, 4D, and Color Doppler technologies can provide valuable additional information in selected cases, they complement rather than replace standard 2D imaging.

For hospitals, diagnostic centers, and obstetric clinics, investing in high-performance ultrasound systems with excellent 2D image quality, reliable probes, and regular maintenance is essential for accurate fetal assessment and quality patient care.

A carefully performed Anomaly Scan not only supports the early recognition of many congenital abnormalities but also provides reassurance to expectant parents when fetal development appears normal. As a cornerstone of modern prenatal ultrasound, it remains one of the most important examinations for promoting maternal and fetal health.