You probably already know how important your mid-pregnancy ultrasound is, but anomaly scan in which week of pregnancy? And what happens if you do it too early or too late?
This guide walks you through the ideal timing, real-world scenarios, common mistakes, and how to make the most of this crucial scan.
Understanding the Anomaly Scan (And Why Timing Matters)
A Quick Overview of the 20-Week Anatomy Ultrasound
The anomaly scan is a detailed ultrasound that checks your baby from head to toe. It examines the brain, spine, heart, kidneys, limbs, placenta, amniotic fluid, and more.
But here’s the thing—your baby needs to be just the right size for the scan to give clear answers. That’s why timing is everything.
Why You Should Care About the Exact Week
Do it too early and critical organs may not be developed enough to evaluate.
Do it too late and the baby becomes so big or curled that the sonographer struggles to get clear views.
You want that perfect window where everything is visible, measurable, and reliable.
Anomaly Scan in Which Week of Pregnancy? The Ideal Time Window
The Recommended Range (And Why It Works)
Most experts recommend doing the anomaly scan between 18 and 22 weeks of pregnancy.
This range offers the best balance of fetal size and organ visibility.
Why 20 Weeks Is the Sweet Spot
At around 20 weeks, your baby’s organs are mature enough for accurate assessment. You get:
- Clear imaging
- Precise growth measurements
- Reliable detection of structural abnormalities
- Time for follow-up tests if needed
How Hospitals Usually Schedule It
Many hospitals automatically set your appointment for 20 weeks to avoid timing mistakes.
But if you’re arranging it privately, you have to be extra careful not to drift outside the recommended window.
Why the Timing of Your Anomaly Scan Can Make or Break Accurate Results
What Happens If You Go Too Early?
Before 18 Weeks: The Risks
If you scan before 18 weeks, the baby’s organs may be underdeveloped. Your report might say:
- “Poor visibility”
- “Repeat scan required”
- “Anatomy incomplete”
An early scan often leads to confusion and unnecessary panic because the doctor may need you to repeat the scan.
What Happens If You Go Too Late?
After 22 Weeks: The Challenges
As the baby grows, space becomes limited. After 22 weeks, it’s harder to capture:
- Heart structures
- Face and brain details
- Spine alignment
- Limb measurements
Moreover, if your healthcare provider finds an issue, you’ll have less time for confirmatory tests.
Signs You Should Do the Scan Sooner Within the Window
If You Have High-Risk Factors
You might consider doing the scan around 18–19 weeks if you have:
- Diabetes
- Hypertension
- Autoimmune diseases
- Previous congenital anomalies
- IVF pregnancy
- Twins or multiples
In such cases, doctors prefer earlier detection so they can plan follow-up care.
If Your Early Pregnancy Dating Scan Was Uncertain
Maybe your last period was irregular. Maybe you weren’t sure about your ovulation date.
In such scenarios, your doctor may adjust the anomaly scan timing based on fetal size.
How to Prepare for Your Anomaly Scan Timing (Without Stressing Out)
Check Your Pregnancy Dates Twice
Don’t rely on memory. Use:
- Your dating scan
- LMP (last menstrual period)
- Your pregnancy app
Being off by even a week can push you out of the ideal window.
Book Your Appointment Early
Hospitals get busy.
If you want a perfect 20-week slot, don’t wait until the last minute.
Track Your Symptoms and Milestones
Not feeling movement yet? Having unusual cramps?
Your doctor might adjust the timing based on what’s happening in your pregnancy.
Common Timing Mistakes (And How to Avoid Them)
1. Waiting Until the Last Week
Many parents assume that “later is clearer.”
But after 22 weeks, visibility drops. Don’t risk blurred results.
2. Getting Confused Between Gestational and Fetal Age
Your doctor counts weeks from your last period, not from conception.
If someone tells you to do the scan “at 20 weeks,” they mean gestational age.
3. Doing the Scan Before Your Doctor Recommends It
Excited to see your baby? That’s normal.
But don’t rush.
A 17-week scan may look exciting but won’t replace the proper anomaly scan.
4. Rescheduling Without Checking Your Gestation
You might push your appointment forward due to travel or work.
Many parents end up unknowingly shifting into the late window.
Table: Best Timing for Anomaly Scan Based on Pregnancy Scenario
| Pregnancy Situation | Recommended Week | Why |
| Low-risk, single pregnancy | 20 weeks | Optimal organ visibility |
| High-risk pregnancy | 18–19 weeks | Early detection for follow-up |
| IVF pregnancy | 19–20 weeks | More detailed cardiac views |
| Twins or multiples | 18–20 weeks | Crowding increases after 20 weeks |
| Uncertain dating | 18–22 weeks | Adjust according to growth |
| Previous congenital anomaly | 18–19 weeks | Extra time for assessments |
Pros & Cons of Scheduling at Different Times
Earlier Side of Window (18–19 Weeks)
Pros:
- Early reassurance
- More time for follow-up tests
- Easier fetal positioning
Cons: - Some structures may still be maturing
Mid-Window (20 Weeks)
Pros:
- Best overall visibility
- Ideal organ development stage
- Most accurate measurements
Cons: - Busy appointment schedules
Later Side of Window (21–22 Weeks)
Pros:
- Baby slightly bigger for measurements
Cons: - Harder imaging
- Less time for diagnostics
- May require repeat scans
What to Expect During the Scan
The Procedure Itself
The sonographer applies gel on your belly and slowly moves the probe.
You’ll see your baby’s:
- Heart beating
- Spine forming
- Brain chambers
- Kidneys
- Face and limbs
The scan usually lasts 30–45 minutes.
If Baby’s Position Isn’t Ideal
Sometimes the baby curls up or faces the wrong way.
You may be asked to:
- Walk around
- Drink water
- Turn sideways
It’s normal and nothing to worry about.
What You Should Do If Your Scan Shows ‘Incomplete Views’
Don’t Panic—It Happens Often
Incomplete views don’t mean anything is wrong.
Common reasons include:
- Baby’s position
- Low amniotic fluid
- Maternal weight
- Shadowing
Follow Your Doctor’s Advice
They may reschedule you within a few days for a repeat scan.
Frequently Asked Questions
1. Anomaly scan in which week of pregnancy should I ideally book it?
Between 18–22 weeks, with 20 weeks being ideal.
2. Can the anomaly scan detect all birth defects?
It detects many structural issues, but not all conditions can be identified on ultrasound.
3. Is fasting needed before the anomaly scan?
No. You don’t need to fast. Eat normally.
4. Will the anomaly scan tell me the gender of my baby?
In some countries, yes. In others, like many parts of South Asia, gender disclosure is restricted by law.
5. What if my baby is not in the right position?
The sonographer will try different angles, or you may be asked to walk or return for a repeat scan.
6. Can I bring someone with me?
Most clinics allow one companion, but it depends on their policy.
7. Will I get photos or a video?
Many clinics provide printed or digital images, but availability varies.
Conclusion
Scheduling your anomaly scan at the right time—ideally around 20 weeks—gives you the clearest, most reliable look at your baby’s development. Understanding the ideal window helps you avoid repeat scans, unclear reports, and unnecessary stress.
Now that you know the perfect timing and how to prepare, you’re ready to plan confidently and enjoy this special moment.
Also Read: 5 Signs of Ovulation Without a Period
