Ultrasound scans use sound waves to build a picture of the baby in the womb.
Most scans are carried out by specially trained staff called sonographers.
The scan is carried out in a dimly lit room so the sonographer is able to get good images of your baby. You'll then be asked to lower your skirt or trousers to your hips and raise your top to your chest.
You'll be given the chance to discuss it with your maternity team before making your decision. You may like someone to come with you to the scan appointment.
Most hospitals do not allow children to attend scans as childcare is not usually available.
If you're offered further tests, you will be given more information about them so you can decide whether or not you want to have them.
You'll be able to discuss this with your midwife or consultant.
If you are overweight or your body tissue is dense, sometimes this can reduce the quality of the image because there is more tissue for the ultrasound waves to get through before they reach the baby.
If it's difficult to get a good image, the scan may take longer or have to be repeated at another time.
This is because most babies are healthy and do not have abnormalities. If a problem is found or suspected, the sonographer may ask for a second opinion from another member of staff.