An ultrasound scan (sonogram) uses sound waves that bounce off solid objects to create two-dimensional black and white images on a screen. It's completely safe for you and your baby.
Scans are mainly done to give your midwife and doctor information about how your baby's growing and developing, but it’s lovely for you and your partner to be able to see them too.
Three-dimensional (3D) and colour scans aren’t routinely used in the NHS.
When will I have an ultrasound scan?
You should be offered at least 2 scans:
You might also be offered a nuchal translucency scan (NT) at your early pregnancy scan to screen for Down’s syndrome.
You can choose not to have these scan – the decision's yours.
What your ultrasound scan can show
Your scan can show:
- your baby’s size, which is important for finding out when they’re due to arrive
- your baby’s heartbeat
- the way your baby's lying in your womb, which is important when you give birth
- whether you’re having twins or more
- how your baby’s organs and bones are developing, including their spine
- where your placenta's lying - If it’s low down or lying across your cervix towards the end of your pregnancy, it can affect how your baby needs to be delivered
The scan can also show some abnormalities or problems, but it’s not always possible to see them.
It’s important to remember that scans aren’t completely accurate – there are some health problems that can’t be picked up by the scan.
Can the scan show the sex of the baby?
The scan isn't done to find out the sex of your baby.
It’s often impossible to tell whether you’re having a boy or a girl because of your baby's position during the scan. It also isn't completely reliable.
Preparing for a scan
You’ll need to have a full bladder before early pregnancy scans (before 16 weeks). That means you’ll need to drink about a pint of water. When your bladder's full, it pushes your womb up so the sonographer can see better.
You don’t need a full bladder before the mid-pregnancy scan (between 18 and 21 weeks).
What happens at the ultrasound scan
To do the scan:
- You'll lie down on a couch and uncover your tummy
- The sonographer will spread some gel on your tummy
- They'll roll a hand-held instrument called a transducer over it - this picks up a picture of everything underneath it and sends it to a screen
If you have questions about what you’re seeing on your ultrasound scan, ask the sonographer to explain.
Most scans are normal. If the sonographer is unsure about the image, they'll tell you and may ask for a second opinion from another sonographer or doctor.
If the sonographer hasn’t been able to see your baby clearly, you may be asked to come back on another day for a repeat scan.