Ultrasound scans
All hospitals must offer women at least two ultrasound scans during their pregnancy. The first is usually when you are around 8-14 weeks pregnant and is sometimes called the dating scan, because it estimates when the 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.
The scans may detect some serious structural abnormalities so you should be prepared for that information, although the majority of scans show that the baby is developing normally.
The dating scan and anomaly scan are offered to all women, but not everyone chooses to have 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 carrying 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).
The dating scan
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 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 structural (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.
Find out more about checks and tests in pregnancy and screening for Down's syndrome.
