Anomaly scan in pregnancy: when it is done, what it looks at, and how to prepare

4 min read

The anomaly scan is an ultrasound that checks how your baby is developing. It is usually done at around 18 to 21 weeks of pregnancy and takes about 30 minutes. It cannot find every condition. Your doctor can explain why and when it is right for you.

A couple watch an ultrasound scan of their baby during pregnancy

At a glance

When
Usually 18 to 21 weeks, sometimes up to 23 weeks
How long
Usually around 30 minutes; longer if the baby is moving or not in a good position
What it is
An ultrasound scan that checks growth and physical development
Preparation
You will be told if you need a full bladder. Arrive early and wear loose clothing
Limits
It may not find everything
Safety
The NHS says there is no known risk to you or your baby
On this page
  1. What the anomaly scan is
  2. When it is done
  3. How to prepare
  4. What the scan can and cannot do
  5. The decision is yours

What the anomaly scan is

It is an ultrasound scan in the middle of pregnancy, also known as the 20-week scan. It checks your baby’s growth and screens for certain serious physical conditions, such as problems of the spine, heart, kidneys, or lip and palate. The placenta and the blood flow in the womb are checked too.

When it is done

Usually between 18 and 21 weeks of pregnancy, and up to 23 weeks in some cases. Your doctor will tell you which week is best; timing can differ a little between hospitals.

How to prepare

  • When you book, ask whether you need a full bladder. If you do, you will be told.
  • Arrive a little early and wear loose clothing.
  • Bring your earlier ultrasound and test reports.
  • Ask the hospital in advance whether someone can come with you.

What the scan can and cannot do

The scan may not find everything. If it shows something, the doctor will explain what it means and what comes next, and may suggest more tests.

The decision is yours

In the UK’s NHS the scan is always offered, but whether to have it is your choice, and you can change your mind later. Ask your doctor questions before you decide.

Your next step

Anomaly scan priority booking

See the days available and the current booking fee, then choose a slot.

See details and book

Common questions

Is an anomaly scan safe?
The NHS says there is no known risk to you or your baby from the scan.
Do I need a full bladder before the scan?
If you do, you will be told. Ask the hospital when you book.
Can the scan find every problem?
No. The scan may not find everything.
How long does it take?
Usually around 30 minutes; longer if the baby is moving or not in a good position.

Sources

More health information