Anomaly Scan (20-Week Pregnancy Scan): Purpose, Procedure, Benefits & What It Detects
What is an Anomaly Scan?
Anomaly Scan, also known as the 20-week scan, Mid-Pregnancy Scan, Level II Ultrasound, or Targeted Fetal Anatomy Scan, is a detailed ultrasound examination performed during pregnancy to evaluate the baby’s anatomy and identify possible structural abnormalities before birth.
This scan carefully examines the baby’s major organs, monitors growth, checks the placenta and amniotic fluid, and provides valuable information about the overall health of the pregnancy.
When is an Anomaly Scan Performed?
The ideal time for an Anomaly Scan is between 18 and 22 weeks of pregnancy. In some specialized fetal medicine centers, it may be performed up to 24 weeks, depending on clinical indications and local practice.
Why is an Anomaly Scan Important?
The primary purpose of an Anomaly Scan is to evaluate the baby’s physical development and detect congenital structural abnormalities as early as possible.
It helps healthcare professionals:
- Assess fetal anatomy in detail
- Monitor fetal growth
- Check placental position
- Evaluate amniotic fluid volume
- Identify certain birth defects
- Plan appropriate prenatal care if abnormalities are detected
What Does an Anomaly Scan Check?
During the examination, the sonographer systematically evaluates:
Brain & Skull
- Skull shape
- Brain ventricles
- Cerebellum
- Midline structures
Face
- Eyes
- Nose
- Lips
- Facial profile
- Cleft lip assessment
Spine
- Cervical spine
- Thoracic spine
- Lumbar spine
- Sacral spine
Heart
- Four-chamber view
- Cardiac rhythm
- Outflow tracts
- Heart position
Chest
- Lungs
- Diaphragm
Abdomen
- Stomach
- Liver
- Bowel
- Abdominal wall
Kidneys & Bladder
- Both kidneys
- Urinary bladder
Limbs
- Arms
- Legs
- Hands
- Feet
- Long bones
Placenta
- Placental location
- Placental appearance
Amniotic Fluid
- Amniotic fluid volume
Umbilical Cord
- Cord insertion
- Number of vessels
What Conditions Can an Anomaly Scan Detect?
Depending on fetal position, image quality, and gestational age, the scan may help identify several structural abnormalities, including:
- Neural tube defects
- Spina bifida
- Anencephaly
- Cleft lip
- Certain congenital heart defects
- Kidney abnormalities
- Abdominal wall defects
- Limb abnormalities
- Skeletal dysplasia
- Hydrocephalus
Not every condition can be detected before birth, and some abnormalities may develop later in pregnancy or be too subtle to identify on ultrasound.
How is the Scan Performed?
The examination is usually performed through the mother’s abdomen using a 2D Convex Ultrasound Probe.
The sonographer applies ultrasound gel to the abdomen and moves the probe to obtain standard anatomical views of the fetus.
If visualization is difficult, additional imaging techniques may occasionally be recommended by the specialist.
Is 4D Ultrasound Required?
No.
Routine fetal anomaly assessment is primarily performed using high-quality 2D ultrasound.
3D or 4D imaging may provide additional views of certain structures, such as the face or limbs, but they are not mandatory for routine anomaly screening. Clinical diagnosis remains based mainly on detailed 2D imaging.
How Long Does the Scan Take?
Most examinations take 30 to 60 minutes, depending on:
- Baby’s position
- Maternal body habitus
- Gestational age
- Need for additional measurements
What Happens if an Abnormality is Found?
If a possible abnormality is identified, additional evaluation may include:
- Repeat ultrasound examination
- Fetal Echocardiography
- Genetic counseling
- Diagnostic testing (when clinically indicated)
- Referral to a fetal medicine specialist
Further management depends on the specific findings.
Frequently Asked Questions (FAQs)
Is the Anomaly Scan safe?
Yes. Diagnostic ultrasound is considered safe during pregnancy when performed by qualified professionals using appropriate clinical guidelines.
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.
Can I know my baby’s gender?
In many cases, the baby’s sex can be identified if the fetal position allows and if this information is permitted and requested according to local regulations.
Which ultrasound probe is commonly used?
A 2D Convex Probe is the standard probe used for routine fetal anatomy assessment.
Conclusion
Anomaly Scan is one of the most important ultrasound examinations during pregnancy. It provides a comprehensive assessment of fetal anatomy, growth, placenta, and amniotic fluid while helping identify many structural abnormalities before birth. Performed between 18 and 22 weeks of pregnancy, this scan plays a crucial role in supporting informed prenatal care and pregnancy management.