Ultrasound scans
Most hospitals will 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 can help to determine when the baby is due. The second scan usually takes place between 18 weeks and 20 weeks, 6 days. 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 mother or babies and can be carried out at any stage of pregnancy. Talk to your midwife, GP or obstetrician about any concerns you have.
What do ultrasound scans check?
An ultrasound scan can be used in several ways:
- To check your baby's measurements. This gives a better idea of how many weeks pregnant you are. This can be useful if you're unsure about the date of your last period or if your menstrual cycle is long, short or irregular. Your due date is likely to be adjusted according to the ultrasound measurements.
- To check whether you're carrying more than one baby.
- To detect some abnormalities, particularly in your baby's head or spine.
- To show the position of your baby and the placenta. For example, when the placenta is low down in late pregnancy, special care may be needed at delivery, or a caesarean section may be advised.
- To check that the baby is growing and developing normally (this is particularly important if you're carrying twins or more).
At the scan
You may be asked to drink a lot of fluid 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 jelly is put on your abdomen. An instrument is 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. It can be very exciting to see a picture of your own baby moving about.
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. Ask if it's possible to have a copy of the picture. 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 20 weeks, 6 days pregnant. The scan checks for possible physical problems (abnormalities) in your baby, although it can't pick up every problem.
The scan is offered to all women, but not everyone chooses to have it. Your choice will be respected if you decide not to have the scan, and you'll be given the chance to discuss it with your maternity team before making your decision.
The anomaly scan is carried out in the same way as the dating scan, with jelly on your tummy and the sonographer passing the ultrasound instrument 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.
Find out more about checks and tests in pregnancy and screening for Down's syndrome.