Anomaly Scan: The Ultimate Guide for Expecting ParentsAnomaly Scan (20-Week Scan): What It Checks, How to Prepare, and How to Read the Report

Quick Answer

The anomaly scan, also called the 20-week scan, is a detailed ultrasound done between 18 and 20 weeks of pregnancy to check your baby's physical development. It examines the brain, spine, heart, face, kidneys, limbs and other organs, checks growth and the placenta, and screens for a set of specific conditions. It is safe, painless and usually takes about 30 minutes. In India, by law, the scan will not reveal your baby's sex.

Key Takeaways

• It is the most detailed routine scan of pregnancy. Done at 18 to 20 weeks (sometimes up to 22 or 23), it checks your baby's anatomy organ by organ.

• It is a screening test, not a guarantee. It detects many conditions but not all. Some, like open spina bifida, are seen clearly (around 90%), while others, like heart defects, are harder (around half).

• Preparation is simple. Wear loose clothing, carry your reports, and have a full bladder only if your clinic specifically tells you to.

• A normal report is reassuring but does not promise a completely problem-free baby, because no scan can see everything.

• In India, the scan cannot tell you the baby's sex. Revealing foetal sex is a criminal offence under the PC-PNDT Act.

What Is an Anomaly Scan?

The anomaly scan is a detailed ultrasound that looks closely at how your baby is developing physically. It is often called the 20-week scan or the mid-pregnancy scan. Using a probe moved over your tummy, the sonographer examines your baby's bones, heart, brain, spinal cord, face, kidneys and abdomen, and also checks your placenta and the blood flow in your uterus (NHS).

Its purpose is twofold: to check that your baby is growing well, and to screen for a set of specific structural conditions. It is one of the most important scans in pregnancy, which is why it is more detailed and takes longer than a routine growth scan. It is part of the wider set of common tests during pregnancy.

When Is the Anomaly Scan Done?

The anomaly scan is usually done between 18 and 20 weeks of pregnancy, and in some cases up to 22 or 23 weeks (NHS). This timing is deliberate: by around 20 weeks, the baby's organs are developed enough to be examined in detail, while there is still time to plan further tests or care if something is found.

If your baby is lying in an awkward position or moving a lot, the sonographer may not be able to complete all the checks, and you might be asked to walk around, eat something, or come back for a second appointment. This is common and does not mean anything is wrong.

How Do I Prepare for the Anomaly Scan?

Preparation is straightforward. This is one of the most searched parts of the topic, so here it is clearly.

• Wear loose, comfortable clothing that lets you expose your tummy easily.

• Carry your maternity notes and previous scan reports.

• Full bladder only if told. Some clinics ask for a full bladder, others do not at this stage. Follow the specific instruction your clinic gives you rather than assuming.

• Arrive a little early to settle in.

• You can bring your partner, though many clinics do not allow young children. Check beforehand.

• Remove a belly piercing if you have one.

• Ask in advance whether you need to pay for printed pictures.

There is no need to fast, and no injection or medicine is involved.

Is the Anomaly Scan Safe? Are There Any Risks?

Yes, it is safe. Ultrasound uses sound waves, not radiation, and there is no known risk to you or your baby from the scan (NHS). It is painless, though the pressure of the probe on a full bladder can feel a little uncomfortable. The scan usually takes about 30 minutes.

What Does the Anomaly Scan Check For?

The scan examines your baby's anatomy systematically and screens for a defined set of physical conditions. In NHS practice, the scan screens for 11 specific conditions, and Indian anomaly scans check for a similar range of structural abnormalities (NHS):

It also measures your baby's growth (including head, abdomen and thigh bone), checks the amniotic fluid, and looks at the position of the placenta.

Important: the anomaly scan is not the test for Down's syndrome. That is screened earlier through the NT scan and double marker test, and confirmed by amniocentesis if needed.

Can the Anomaly Scan Detect Everything?

No, and this is important to understand so a normal report is not misread as a cast-iron guarantee. It is a screening test. Some conditions are seen clearly and others are much harder to detect (NHS):

• Open spina bifida: around 90% are detected.

• Serious heart defects: around half are detected, because the heart is complex and hard to image.

• Some conditions cannot be seen at all on this scan, and some develop or become visible later.

So a normal anomaly scan is genuinely reassuring, but it means "no problems were seen today", not "your baby is guaranteed to have no health condition of any kind". If anything feels wrong later in your pregnancy, always tell your doctor regardless of a normal scan.

How Do I Read and Understand My Anomaly Scan Report?

Anomaly scan reports are full of measurements and abbreviations, which is why so many parents search for what they mean. Here is a plain-language guide to the common terms.

"No gross fetal anomaly seen" or "NAD" is good news. It is the phrase most parents are looking for and means the scan did not find a major structural abnormality. If your report uses terms you do not understand, ask the doctor who ordered the scan to walk you through it. Never try to self-diagnose from a single measurement, because these are interpreted together and against your dates.

Will the Anomaly Scan Tell Me My Baby's Sex?

In India, no. It is illegal. Under the Pre-Conception and Pre-Natal Diagnostic Techniques (PC-PNDT) Act, no scan, doctor or clinic may reveal the sex of the foetus. This applies to the anomaly scan just as it does to every other scan. A trustworthy clinic will not tell you, and you should not ask, because the law exists to prevent sex-selective practices. Any report or person offering to reveal the baby's sex is acting illegally.

What Happens If the Anomaly Scan Finds Something?

First, try not to panic. Many findings are minor, some are "soft markers" that turn out to be nothing, and even when something significant is found, knowing early allows the best possible planning.

If the scan finds signs of a condition (NHS):

• You will be told after the checks are complete, and often a second team member will review the images.

• You may be offered further scans or tests, such as a detailed fetal echo for the heart, or amniocentesis or chorionic villus sampling for chromosomal conditions.

• You will be referred to a specialist, often a maternal-fetal medicine expert, who will explain what the finding means and your options.

• You will be given counselling and support to make decisions, which are always yours to make.

Getting a concerning result is frightening, and you are entitled to clear explanations and unhurried support, not just a report.

Anomaly Scan: Frequently Asked Questions

"How should I prepare for my anomaly scan?"
Wear loose clothing, carry your maternity notes and earlier reports, and arrive a little early. Only drink up for a full bladder if your clinic specifically asks you to. No fasting or medicine is needed.

"Is the anomaly scan painful or risky?"
It is painless and there is no known risk to you or your baby, as ultrasound uses sound waves, not radiation. The probe pressure may feel slightly uncomfortable, especially on a full bladder, but that is all.

"What does 'no gross anomaly detected' mean on my report?"
It means the scan did not find any major structural abnormality in your baby. It is a reassuring result. Remember that no scan can detect every possible condition, so it means nothing concerning was seen, not an absolute guarantee.

"Can the anomaly scan tell me if it is a boy or girl?"
Not in India. Revealing the sex of the foetus is a criminal offence under the PC-PNDT Act, so no scan or clinic will tell you, regardless of what the scan can technically see.

"Does a normal anomaly scan mean my baby is completely healthy?"
It is very reassuring, but not an absolute guarantee. Some conditions cannot be seen on this scan, and some appear later. Continue your antenatal care and report any concerns to your doctor.

"What if my baby will not stay still during the scan?"
This is common. You may be asked to walk around, eat something, or come back later so the sonographer can complete all the checks. It does not mean anything is wrong.

"Is the anomaly scan the same as the Down's syndrome test?"
No. Down's syndrome is screened earlier, through the NT scan and double marker test, and confirmed if needed by amniocentesis. The anomaly scan focuses on your baby's physical structure, though it may note markers that prompt further testing.

When To Speak To Your Doctor

• If you have not had an anomaly scan and you are between 18 and 23 weeks, tell your doctor so it can be arranged.

• If your report contains terms you do not understand, ask the doctor who ordered it to explain, rather than interpreting a single number yourself.

• If the scan finds something, ask for a clear explanation and a referral to a specialist.

• If anything feels wrong later in pregnancy, report it even if your anomaly scan was normal.

This article is for information only and does not replace the advice of the doctor interpreting your specific scan.

Bottom Line

The anomaly scan at 18 to 20 weeks is the most detailed routine look at your baby's development, checking the brain, spine, heart, face, kidneys, limbs and growth, and screening for a defined set of conditions. It is safe and painless, and preparing for it is as simple as loose clothing and your reports. Remember two things: it is a screening test that cannot catch everything, so a normal report means "nothing concerning was seen" rather than a total guarantee, and in India it will never reveal your baby's sex. If a finding does come up, early detection is what makes good planning and support possible.

References

All links verified live on 17 September 2026.

1. 20-week screening scan — NHS, UK. Source for the timing (18 to 21 weeks, up to 23 in some cases), the 11 conditions screened, the organs examined, detection rates (spina bifida ~90%, heart defects ~50%), preparation, safety, and what happens if something is found.

2. Ultrasound scans in pregnancy — NHS, UK. Supporting reference on pregnancy ultrasound.

3. PC-PNDT Act (Pre-Conception and Pre-Natal Diagnostic Techniques Act) — Government of India. Basis for the prohibition on revealing foetal sex. (Team: link to the official implementing-authority page, as used in Mylo's amniocentesis article.