Most hospitals will offer women at least two ultrasound scans during their pregnancy. The first is usually at around eight to 14 weeks 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 and 20 weeks and is called the anomaly scan because it checks for structural abnormalities.
Ultrasound scans use soundwaves 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. If you have any concerns about having a scan, talk to your midwife, GP or obstetrician. 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).
You'll probably 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.
Video: antenatal screening
Antenatal screening helps you manage your pregnancy better and lets you know how your baby is progressing. In this video an expert talks about what screening involves, and you can watch one woman go for her 20-week scan, and another talk about how screening detected spina bifida in one of her twins.
