The anomaly scan: sometimes called the anatomy or 20-week scan, is one of the most detailed check-ups your baby will have in the womb. It is a careful, structured look at how they are growing, organ by organ.
This guide explains what is checked, what to expect on the day, and what the findings mean, including the small number of scans that flag something worth a closer look.
- Preparation and check-in5 min
- Structural check20 min
- Measurements, fluid & placenta8 min
- Findings and your plan7 min
View as table
| Part of the visit | Typical time |
|---|---|
| Preparation and check-in | about 5 minutes |
| Structural check | about 20 minutes |
| Measurements, fluid & placenta | about 8 minutes |
| Findings and your plan | about 7 minutes |
01What the anomaly scan is
The anomaly scan is a comprehensive ultrasound examination, usually carried out between 18 and 24 weeks. Unlike the dating scan earlier in pregnancy, it is not primarily about timing. It is a detailed evaluation of your baby’s organs and systems, looking for the physical markers of common structural conditions.
Think of it as a thorough progress check: most scans confirm that everything is developing typically, and give you and your baby a clean bill of health at this stage.
Most anomaly scans are reassuring: the value is in checking properly, so that reassurance means something.
The pregnancy scanning team
02What is checked
A senior specialist sonographer works through your baby systematically.
- Detailed foetal anatomy, brain, spinal cord, face, heart, abdomen, kidneys, bladder, arms and legs.
- Foetal biometry, head circumference, abdominal circumference and femur length, used to estimate your baby’s weight and plot their growth.
- Amniotic fluid, checked for volume, an indicator of your baby’s wellbeing.
- Placenta position, including whether it is low-lying, which can affect how you deliver.
- Cervical assessment, usually done over your abdomen, checking for signs that could suggest preterm labour.
If you would like to know your baby’s sex and they are in a good position, your sonographer can tell you during this scan too. This anatomy check is more detailed than the one done during an earlier gender and wellbeing scan.
03What to expect on the day
The scan is straightforward and non-invasive.
- 1
Preparation
You may be asked to come with a full bladder, around four glasses of water 45 minutes beforehand usually does it, as this can improve image clarity.
- 2
The scan
Gel is applied to your abdomen and a transducer moved across your skin, sending safe, high-frequency sound waves that build a picture of your baby.
- 3
Duration
The scan usually takes 30 to 40 minutes, a little longer if your baby is in an awkward position or moving about.
- 4
Findings and your plan
Your sonographer explains what they found and what it means, face to face, before you leave.
04Potential findings
In most cases, the scan confirms typical growth and normally functioning organs. Occasionally it detects something that needs a closer look, including:
- Chromosomal markers, features associated with conditions such as Down’s syndrome or trisomy 18.
- Structural findings, for example, a congenital heart defect, spina bifida or a limb difference.
- Growth concerns, a baby measuring smaller or larger than expected for their dates.
If anything is suspected, we prioritise a prompt referral to a foetal medicine specialist, so you get expert input as quickly as possible.
05Accuracy and limitations
The anomaly scan is thorough, but it is not infallible. Your baby’s position, the amount of amniotic fluid, your body type and any scar tissue can all affect visibility, and some conditions, particularly some heart conditions: may not be detectable until later. Your sonographer will explain any limitations that applied to your scan.
06Interpreting your results, and support if you need it
After the scan, your sonographer talks you through the findings there and then; images are sent to you as well. Most scans are reassuring and need no further action. If something does need a second look, we arrange it, whether that is a further scan, planning for care after birth, or delivery at a specialist unit.
