Why Does an Antenatal Ultrasound Take Longer Sometimes?

By Dr. Rekha – Fetal Medicine Specialist

One of the most common concerns I hear in my scan room is:

“Doctor, why is my scan taking so long? Is something wrong?”

Let me reassure you — in most cases, a longer ultrasound does not mean something is wrong.
In fact, it often means we are being extra careful and thorough.

Let’s understand why.

First, What Is an Antenatal Ultrasound?

An antenatal ultrasound is a detailed imaging test that helps us assess:

• Baby’s growth
• Structural development
• Placenta and amniotic fluid
• Blood flow (in certain scans)
• Overall well-being

Some ultrasounds are routine growth scans, while others — like the NT scan or the Anomaly scan — are detailed structural evaluations that naturally take more time.

Why Does It Sometimes Take Longer?

Here are the most common reasons:

1️⃣ Baby’s Position

This is the most frequent reason.

Babies move, curl up, turn away, or hide their face.
If we need to see:

• The heart
• Spine
• Face
• Brain structures

And the baby is not in an ideal position, we may:

• Wait for baby to move
• Ask you to change position
• Ask you to walk for a few minutes or eat something
• Repeat certain views

It’s not a problem — just patience and positioning.

2️⃣ Detailed Evaluation of Organs

Some scans require checking:

• All four chambers of the heart
• Brain structures in multiple planes
• Spine from neck to tailbone
• Limbs and fingers
• Blood flow patterns

Each organ has to be evaluated carefully and documented.
Precision takes time.

3️⃣ Maternal Factors

Sometimes imaging depends on:

• Abdominal wall thickness
• Scar from previous surgery
• Fibroids
• Reduced amniotic fluid
• Anterior placenta (placenta in front)

These factors can make visualization slightly more challenging, requiring more time.

4️⃣ Advanced or Specialized Scans

Certain ultrasounds are more complex:

• Fetal echocardiography (detailed heart scan)
• Doppler studies
• Growth restriction monitoring
• Twin pregnancy evaluation
• High-risk pregnancy surveillance

These are naturally longer because they involve more measurements and analysis.

5️⃣ Double-Checking for Accuracy

In fetal medicine, we follow a principle:

“Measure twice. Confirm twice. Report once.”

If something appears borderline or unclear, we:

• Re-check
• Change angle
• Re-measure
• Compare with gestational age charts

This is done to avoid both over-diagnosis and under-diagnosis.

Accuracy is more important than speed.

6️⃣ Documentation and Reporting

Behind every scan image, there is:

• Measurement recording
• Growth percentile calculation
• Image labeling
• Structured reporting

Sometimes what seems like “waiting time” is actually detailed documentation happening in real time.

7️⃣ When There Is a Suspicion

If we detect:

• Increased NT
• Structural anomaly
• Soft markers
• Growth concerns
• Abnormal Doppler

We will spend extra time evaluating:

• Related structures
• Associated abnormalities
• Severity
• Need for further testing

This additional time ensures you receive the most complete assessment possible.

Does a Longer Scan Mean Something Is Wrong?

Not necessarily.

In fact, most prolonged scans are due to:

• Baby’s position
• Need for better images
• Thorough evaluation

Silence in the scan room does not mean bad news.
It often means deep concentration.

How Can You Help During the Scan?

• Stay relaxed
• Follow position-change instructions
• Inform us if you feel discomfort
• Be patient

Your cooperation helps us obtain clearer images.

Why Thoroughness Matters

A detailed scan helps in:

• Early detection of abnormalities
• Planning delivery in appropriate centers
• Counseling parents
• Improving outcomes
• Providing reassurance when everything is normal

A few extra minutes today can make a significant difference in care.

Final Reassurance for Expecting Parents

Ultrasound is not just about taking pictures.
It is about:

• Assessing life
• Monitoring development
• Detecting concerns early
• Providing guidance

If your scan takes longer, remember:

It is time invested in your baby’s safety.

And that time is always worth it.

Frequently Asked Questions (FAQs)

Why Does an Antenatal Ultrasound Take Longer Sometimes?

1. Is it normal for my pregnancy scan to take 30–45 minutes?

Yes, absolutely.
Certain scans like the NT scan (first trimester screening) or Anomaly scan (detailed structural scan) are comprehensive evaluations and naturally take longer than routine growth scans.

A detailed scan requires careful assessment of multiple organs, measurements, and documentation.

2. Does a longer scan mean something is wrong with my baby?

Not necessarily.

In most cases, a longer scan happens because:

• Baby is not in an ideal position
• We need clearer images
• We are double-checking measurements
• It is a detailed evaluation

Silence or extra time usually means concentration — not concern.

3. Why does the doctor keep asking me to turn or walk?

Babies move and change position.
If a structure like the heart, face, or spine is not clearly visible, we may:

• Ask you to turn sideways
• Ask you to empty your bladder
• Suggest walking for a few minutes or eating

This helps improve visualization and avoids unnecessary repeat scans.

4. Why is the heart scan taking longer than other parts?

The fetal heart is small and beats very fast.
A detailed heart evaluation requires proper positioning and checking:

• Four chambers
• Outflow tracts
• Blood flow patterns

This requires precision and sometimes extra time.

5. Why does the scan take longer in overweight mothers?

Ultrasound waves pass through tissue.
Increased abdominal wall thickness can sometimes make images less sharp, requiring:

• More time
• Different probe angles
• Additional attempts for clarity

This is purely technical and not related to baby’s health.

6. Why is a twin pregnancy scan longer?

In twin pregnancies, we must assess:

• Each baby separately
• Growth of both babies
• Placenta type
• Fluid levels around each baby
• Blood flow patterns

Naturally, evaluating two babies takes more time than one.

7. Why do you repeat measurements multiple times?

Accuracy is extremely important in fetal medicine.
We repeat measurements to:

• Confirm findings
• Reduce reporting errors
• Ensure proper growth assessment
• Avoid unnecessary anxiety

Precision protects both mother and baby.

8. Why is the doctor quiet during the scan?

During detailed evaluation, concentration is essential.
Silence often means:

• Focusing
• Measuring
• Documenting
• Cross-checking

It does not automatically indicate a problem.

9. Can a long scan harm the baby?

No.
Diagnostic ultrasound used in pregnancy is safe when performed appropriately by trained specialists.

There is no evidence that routine medical ultrasound causes harm.

10. What if the doctor finds something abnormal?

If something unusual is detected:

• We will evaluate it thoroughly
• Explain findings clearly
• Discuss next steps
• Guide you regarding further tests (if needed)

You will never be left without explanation.

11. Should I worry if I am called again for repeat images?

Sometimes repeat scans are required because:

• Baby position was not favorable
• Certain views were incomplete
• Clarity was insufficient

This is common and done for completeness — not necessarily because something is wrong.

Final Message to Parents

A longer scan means:

• Care
• Attention
• Thoroughness
• Safety

It is time invested in ensuring your baby’s healthy development.

Patience during the scan allows us to give you the most accurate and reassuring information possible.