The 20-week scan: what it checks and what to expect

The 20-week scan is a detailed check of your baby’s development, and for many people it’s the scan they look forward to most. Here’s what it checks, what it can’t see, and what to expect on the day.

When and why

The NHS says a 20-week scan is always offered. It is usually done at 18 to 21 weeks, and it is also called the anomaly scan or mid-pregnancy scan. It is your choice whether to have it. If you decline, you can ask your midwife or GP later whether you can still have one.

What it checks

This describes the NHS in England. Scotland, Wales and Northern Ireland have their own screening programmes with similar timings, so check with your midwife what you’ll be offered.

The NHS says the scan looks for 11 conditions:

anencephaly, open spina bifida, cleft lip and palate
diaphragmatic hernia, gastroschisis, exomphalos
serious heart problems, bilateral renal agenesis, severe skeletal dysplasia
Edwards’ syndrome and Patau’s syndrome

The sonographer looks at your baby’s bones, heart, brain, spinal cord, face, kidneys and stomach, plus your placenta and the blood flow in your womb.

The scan can’t find every condition. Some are easier to see than others, and a normal scan can’t promise everything is fine.

On the day

It usually takes about 30 minutes, longer if your baby is moving a lot or is in an awkward position.
You may be asked to walk around or have something to eat and come back.
If the pictures still aren’t clear, you’ll be offered another appointment before 23 weeks.
You’ll be told whether you need a full bladder.
You can bring someone, but most hospitals don’t allow children. Check with the hospital first.
Wear loose clothing, and take out any belly piercing.

The NHS says there is no known risk to you or your baby from the scan.

Will I find out the sex?

You may be asked whether you want to know. It isn’t guaranteed, because your baby’s position can make it impossible to see.

If something is found

Most people are told there are no signs of a condition. If signs are found, you’ll be told after the scan, and may be offered more scans or tests such as amniocentesis or CVS, and a referral to a specialist. These later tests can confirm whether a condition is present. You’ll be supported whatever you decide. See what a higher chance result means.

Antenatal Results and Choices (ARC) offers free, non-directive information and support. Its helpline is 020 7713 7486, Monday to Friday, 10am to 5.30pm, with calls on Tuesday and Thursday evenings (8pm to 10pm) arranged by emailing info@arc-uk.org. You can also text 07908 683004 (UK only).

Questions people ask

Can I miss the 20-week scan?

It’s optional. Tell your midwife if you’d rather not have it.

Does it check my baby’s growth?

It looks at growth and your placenta. If there are concerns about growth later, you may be offered more scans. See growth scans.

What if the pictures aren’t clear?

The NHS says you’ll be offered another appointment before 23 weeks.

Will I feel my baby move by then?

Many people start to feel movements around this time. See first baby movements.