For many women, ultrasound scans are the highlight of pregnancy. It's very exciting and moving to 'see' your baby in the womb, often moving his or her hands and legs.
Hospitals routinely offer women at least two ultrasound scans during their pregnancy. The first is usually when you're around 12 weeks pregnant and is sometimes called the dating scan, because it estimates when your baby is due (the estimated date of delivery, or EDD).
The second scan usually takes place between 18 weeks and 21 weeks. It's called the anomaly scan because it checks for structural abnormalities (anomalies) in the baby.
Ultrasound scans use sound waves to build a picture of the baby in the womb. The scans are completely painless, have no known side effects on mothers or babies and can be carried out at any stage of pregnancy. Talk to your midwife, GP or obstetrician about any concerns you have.
Although having a scan in pregnancy is usually a happy event, be aware that ultrasound scans may occasionally detect some serious abnormalities, so you should be prepared for that information.
The dating scan and anomaly scan are offered to all women, but you don't have to accept them. Your choice will be respected if you decide not to have the scans, and you'll be given the chance to discuss it with your maternity team before making your decision.
What can an ultrasound scan be used for?
An ultrasound scan can be used in several ways:
- To check your baby's size. At the dating scan, this gives a better idea of how many weeks pregnant you are. Your due date will be adjusted according to the ultrasound measurements.
- To check whether you're having more than one baby.
- To detect most abnormalities.
- To show the position of your baby and the placenta. For example, when the placenta is low down in late pregnancy, a caesarean section may be advised.
- To check that the baby is growing normally (this is particularly important if you're carrying twins or you have had problems in this pregnancy or a previous pregnancy).
What happens during an ultrasound scan in pregnancy?
You may be asked not to go for a wee (urinate) before you have the scan. A full bladder pushes your womb up and this gives a better picture.
You then lie on your back and some lubricating gel is put on your abdomen. A small device is then passed backwards and forwards over your skin, and high-frequency sound is beamed through your abdomen into the womb. The sound is reflected back and creates a picture, which is shown on a TV screen.
Ask for the picture to be explained to you if the image seems confusing. It should be possible for your partner to come with you and see the scan. Many couples feel that this helps to make the baby seem real for them both. You may be able to have a picture of your baby – there might be a small charge for this.
The 20 week (anomaly) scan
This is a detailed ultrasound scan, usually carried out when you are between 18 weeks and 21 weeks pregnant. The scan checks for major physical abnormalities in your baby, although it can't pick up every problem.
The anomaly scan is carried out in the same way as the dating scan, with gel on your tummy and the sonographer passing the ultrasound device backwards and forwards. Sometimes, the sonographer doing the scan will need to be quiet while they concentrate on checking your baby. However, they will be able to talk to you about the pictures once they've completed the check. Most hospitals welcome partners into the scan room. You need to check this with your hospital.
Is it a girl or boy?
If you want to find out the sex of your baby, you can usually do so during the 20 week scan.
Tell the sonographer that you'd like to know your baby's sex at the start of the scan. Be aware, though, that it's not always possible for the sonographer to be 100% certain about your baby's sex. For example, if your baby is lying in an awkward position, it may be difficult or impossible to tell whether your baby is male or female.
Some hospitals have a policy of not telling patients the sex of their baby. If your hospital does not routinely inform parents about their baby's sex, you may be able to pay privately for a scan to find out. Speak to your sonographer or midwife to find out more.
Some hospitals will sell you a copy of your scan image so you can show everyone the very first pictures of your baby.
Find out more about checks and tests in pregnancy and screening for Down's syndrome.