Prenatal Care 12 min read

Preparing for Your 20-Week Anatomy Scan: What to Expect

The 20-week anatomy scan is one of the most comprehensive and exciting ultrasounds of your pregnancy. This detailed examination provides crucial information about your baby's development and gives many parents their first clear look at their little one. Here's everything you need to know to prepare for this important milestone.

By Dr. Amanda Rodriguez, PhD

The 20-week anatomy scan, also known as the level II ultrasound or anomaly scan, is typically performed between 18-22 weeks of pregnancy. This comprehensive examination is designed to evaluate your baby's growth and development, screen for potential birth defects, and assess the placenta and amniotic fluid levels.

For many expectant parents, this scan represents a pivotal moment in their pregnancy journey - often when they learn their baby's sex and see detailed images that make the pregnancy feel more real. Understanding what to expect can help you prepare both practically and emotionally for this significant appointment.

Why the 20-Week Anatomy Scan is Important

Comprehensive Health Assessment

This scan provides the most detailed evaluation of your baby's anatomy during pregnancy, examining all major organ systems and structures.

Early Detection of Abnormalities

Many birth defects and developmental issues can be identified at this stage, allowing for early intervention planning and specialized care.

Growth and Development Tracking

Measurements help ensure your baby is growing at an appropriate rate and can identify potential growth restrictions.

Pregnancy Monitoring

Assessment of placental position, amniotic fluid levels, and cervical length provides important information about pregnancy health.

What Structures Are Examined

During the anatomy scan, the sonographer will systematically examine multiple aspects of your baby's development:

Head and Brain

  • Brain hemispheres and ventricles
  • Cerebellum development
  • Skull shape and closure
  • Facial structures (eyes, nose, lips)
  • Measurement of head circumference

Screens for: Neural tube defects, hydrocephalus, facial clefts

Heart and Circulation

  • Four-chamber heart view
  • Heart rate and rhythm
  • Major blood vessels
  • Blood flow patterns

Screens for: Congenital heart defects, arrhythmias

Spine and Neural System

  • Vertebrae alignment
  • Spinal cord development
  • Skin covering completeness

Screens for: Spina bifida, spinal malformations

Limbs and Movement

  • Arm and leg length measurements
  • Hand and foot development
  • Joint mobility
  • Movement patterns

Screens for: Limb defects, skeletal abnormalities

Abdominal Organs

  • Stomach, kidneys, bladder
  • Liver and gallbladder
  • Bowel development
  • Abdominal wall integrity

Screens for: Kidney problems, abdominal wall defects

Sex Determination

  • External genitalia examination
  • Gender identification (if desired)

Accuracy: 95-99% at this stage

Pregnancy and Placental Assessment

Placental Evaluation

Location Assessment

  • Distance from cervix
  • Identification of placenta previa
  • Blood vessel positioning

Placental Health

  • Texture and appearance
  • Blood flow evaluation
  • Size appropriate for gestational age

Amniotic Fluid Assessment

Fluid Volume (AFI - Amniotic Fluid Index)

  • Normal: 5-25 cm
  • Oligohydramnios: Too little fluid (<5 cm)
  • Polyhydramnios: Too much fluid (>25 cm)

Fluid Quality

  • Clarity assessment
  • Presence of debris or particles

Cervical and Uterine Assessment

  • Cervical length measurement
  • Cervical opening (dilation)
  • Uterine fibroid identification
  • Overall uterine shape

How to Prepare for Your Anatomy Scan

Before Your Appointment

Scheduling Considerations

  • Allow 45-60 minutes for the complete scan
  • Schedule when your partner can attend if desired
  • Consider childcare for other children
  • Plan for potential follow-up appointments

Physical Preparation

  • Wear comfortable, easily removable clothing
  • Two-piece outfits work best for abdominal access
  • You may need to drink water beforehand (follow specific instructions)
  • Some facilities recommend a light meal to encourage fetal activity

Documentation

  • Bring insurance cards and identification
  • List of current medications
  • Previous ultrasound reports if from different facility
  • Questions you want to ask

Emotional Preparation

  • Discuss expectations with your partner
  • Prepare for the possibility of needing additional testing
  • Consider whether you want to learn the baby's sex
  • Plan celebration activities for after the appointment

What Happens During the Scan

1

Check-in and Preparation

You'll complete any necessary paperwork and may be asked about your medical history. You'll then be taken to the ultrasound room and asked to lie on an examination table.

2

Gel Application and Positioning

Warm ultrasound gel will be applied to your abdomen. The sonographer will position the ultrasound transducer and begin the examination.

3

Systematic Examination

The sonographer will methodically examine all fetal structures, taking measurements and capturing images. This is the longest part of the procedure.

4

Image Review and Discussion

The sonographer may explain what you're seeing on the screen and answer basic questions. However, detailed results interpretation is typically done by your doctor.

5

Report Completion

Images and measurements are compiled into a report for your healthcare provider. You may receive some images to take home.

Tips for the Best Scan Experience

  • Stay relaxed: Tension can make it harder to get clear images
  • Ask questions: Don't hesitate to ask what you're seeing
  • Be patient: Baby's position may require waiting or repositioning
  • Enjoy the moment: This is a special opportunity to see your baby
  • Take photos/videos if allowed: Many facilities permit this

Understanding Measurements and Growth Assessment

Standard Fetal Measurements

Biparietal Diameter (BPD)

What it measures: Width of the baby's head

Normal at 20 weeks: ~4.7-5.2 cm

Used for: Dating accuracy, head growth assessment

Head Circumference (HC)

What it measures: Circumference around the baby's head

Normal at 20 weeks: ~17-19 cm

Used for: Brain development assessment

Abdominal Circumference (AC)

What it measures: Circumference around baby's abdomen

Normal at 20 weeks: ~15-17 cm

Used for: Growth assessment, organ development

Femur Length (FL)

What it measures: Length of the thigh bone

Normal at 20 weeks: ~3.2-3.8 cm

Used for: Dating confirmation, limb development

Estimated Fetal Weight (EFW)

Using the above measurements, the ultrasound software calculates an estimated fetal weight:

  • At 20 weeks: Approximately 300-400 grams (10-14 ounces)
  • Percentile ranking: Shows how your baby compares to others at the same gestational age
  • Growth trajectory: Compared to previous ultrasounds to assess growth rate

Understanding Percentiles

10th-90th percentile Normal range
<10th percentile Small for gestational age (may need monitoring)
>90th percentile Large for gestational age (may need monitoring)

Understanding Potential Findings

Normal Variations vs. Abnormalities

Common Normal Findings

  • Choroid plexus cysts: Small, fluid-filled spaces in the brain (usually resolve)
  • Echogenic bowel: Bright appearance of intestines (often normal)
  • Single umbilical artery: Two vessels instead of three (usually benign)
  • Mild kidney dilation: Slight enlargement of kidney collecting system

Findings Requiring Follow-up

  • Growth restrictions: Baby measuring small for gestational age
  • Placenta previa: Placenta covering the cervix
  • Abnormal amniotic fluid levels: Too much or too little fluid
  • Structural abnormalities: Heart defects, neural tube defects

Detection Rates and Limitations

The anatomy scan can detect approximately 60-70% of major structural abnormalities, but it's important to understand its limitations:

High Detection Rates (>90%)

  • Neural tube defects (spina bifida)
  • Major heart defects
  • Limb deficiencies
  • Abdominal wall defects

Moderate Detection Rates (50-90%)

  • Kidney abnormalities
  • Facial clefts
  • Some chromosome abnormalities

Lower Detection Rates (<50%)

  • Hearing or vision problems
  • Intellectual disabilities
  • Some genetic conditions
  • Minor structural abnormalities

After Your Anatomy Scan

Receiving Your Results

Immediate Feedback

The sonographer may share basic observations during the scan, but cannot provide medical interpretations or diagnoses.

Preliminary Report (Same Day)

A preliminary report is often available immediately, though your doctor will provide the complete interpretation.

Doctor's Review (1-3 Days)

Your healthcare provider will review the complete report and contact you with results, usually within 1-3 business days.

If Additional Testing is Recommended

Repeat Ultrasound

When needed: Poor visualization, baby's position, or to monitor specific findings

Timing: Usually 2-4 weeks later

Specialized Ultrasound

When needed: Complex abnormalities requiring specialist evaluation

Who performs: Maternal-fetal medicine specialist

Genetic Counseling

When needed: Abnormalities suggesting genetic conditions

Purpose: Risk assessment and testing options discussion

Amniocentesis

When considered: Suspected chromosomal abnormalities

Timing: Can be performed from 15-20 weeks

Important Questions to Ask

During the Scan

  • "Can you show me the baby's heart beating?"
  • "What structures are you examining now?"
  • "Is the baby in a good position for measurement?"
  • "Can you tell us the baby's sex?" (if you want to know)
  • "Are you able to see everything you need to?"

About Results

  • "When will I receive the complete results?"
  • "Who will explain the results to me?"
  • "What happens if something abnormal is found?"
  • "Are the measurements normal for this gestational age?"
  • "Is my due date still accurate based on these measurements?"

Follow-up Care

  • "Will I need any additional ultrasounds?"
  • "When is my next prenatal appointment?"
  • "Are there any special precautions I should take?"
  • "What signs should I watch for and report?"

Coping with Anxiety and Concerns

Managing Pre-Scan Anxiety

Information Gathering

Learn about the procedure beforehand, but avoid excessive internet searching that may increase anxiety.

Support System

Bring your partner or a supportive friend to the appointment for emotional support.

Relaxation Techniques

Practice deep breathing, meditation, or other relaxation methods before and during the scan.

Positive Focus

Remember that the vast majority of anatomy scans show normal, healthy development.

If Abnormalities Are Found

Immediate Steps

  • Ask for clear explanation of findings
  • Request information about next steps
  • Don't hesitate to ask questions
  • Take notes or bring someone to help remember information

Emotional Support

  • Allow yourself to feel whatever emotions arise
  • Seek support from family, friends, or counselors
  • Connect with support groups for specific conditions
  • Consider genetic counseling for comprehensive information

Moving Forward

  • Focus on obtaining accurate, complete information
  • Consider all available options
  • Seek second opinions if desired
  • Make decisions based on your values and circumstances

Advances in Ultrasound Technology

3D and 4D Ultrasound

Traditional 2D Ultrasound

  • Flat, cross-sectional images
  • Best for medical assessment
  • Standard for anatomy scans
  • Most accurate for measurements

3D Ultrasound

  • Three-dimensional surface images
  • Better visualization of facial features
  • Helpful for certain abnormalities
  • Enhanced bonding experience

4D Ultrasound

  • Real-time 3D images (video)
  • Shows baby's movements
  • May capture facial expressions
  • Popular for keepsake videos

Doppler Ultrasound

This technology measures blood flow and may be used during anatomy scans to:

  • Assess heart function and rhythm
  • Evaluate umbilical cord blood flow
  • Check circulation in major vessels
  • Identify potential circulation problems

Making the Most of Your Anatomy Scan

The 20-week anatomy scan is a milestone moment in your pregnancy journey. This comprehensive examination provides invaluable information about your baby's development and can offer tremendous reassurance about their health and growth.

While the technical aspects of the scan are important, don't forget to enjoy this special opportunity to see your baby in detail. Many parents describe this as the moment their pregnancy became "real" - seeing their baby's profile, counting fingers and toes, and perhaps learning whether they're having a boy or girl.

Remember that the vast majority of anatomy scans reveal healthy, normally developing babies. If any concerns are identified, modern medicine offers many options for monitoring, treatment, and support. Trust in your healthcare team, ask questions when you need clarification, and lean on your support system throughout this important part of your pregnancy journey.

Related Articles

20-Week Fetal Development

What your baby looks like at 20 weeks gestation

High-Risk Pregnancy Care

When specialized care is needed during pregnancy

Pregnancy FAQ

Common questions about prenatal testing and care
Medical Disclaimer: This article is for educational purposes only and should not replace professional medical advice. Ultrasound interpretation requires specialized medical training, and results should always be discussed with qualified healthcare providers. Every pregnancy is unique, and individual circumstances may affect scan recommendations and results. Always follow your healthcare provider's specific instructions and seek medical attention for any concerns about your pregnancy or ultrasound findings.