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As well as giving doctors information about how your fetus is developing, an ultrasound scan is your first chance to get to know your baby. As Dr David Liu, obstetrician, says, provided all is well, a scan can help.
How ultrasound works
Ultrasound scans give doctors a two-dimensional picture of your baby. High-frequency soundwaves are sent though your abdomen using a device called a transducer. These waves bounce off your baby and back to a computer, which are translated into a picture.
Ultrasound scans are offered at different stages of pregnancy for various reasons. The timing of your scans, and how often you have them, will depend on how your pregnancy is progressing and on your hospital's policy on ultrasound scans.
Early scan
These are sometimes offered between six and 11 weeks if you have a history of miscarriage, if you are experiencing bleeding or pain, or if you've had fertility treatment. The sonographer may use a special scanning probe, which is placed in your vagina, as ordinary equipment may not be able to detect your baby yet.
Dating scan
This is offered by some, but not all, hospitals to help doctors accurately date your pregnancy and is generally done between 11 and 16 weeks, but can be done as early as seven weeks. You will probably have a 'pelvic' ultrasound, where the transducer is placed on the skin over your pelvis. You may be asked to drink lots of water before the appointment, because your uterus (womb) can be seen more easily when your bladder is full. Your sonographer will give a commentary on what she can see and freeze frames to take measurements - you can also ask for a picture to take home!
Nuchal scan
Done between 10 and 13 weeks, this scan tells you your risk of having a baby with Down's syndrome by measuring fluid accumulation at the back of your baby's neck. Your doctor will use the scan measurement, your age and a blood test to calculate your risk. If the risk is higher than one in 300, you may be offered a diagnostic test such as chorionic villi sampling (where cells are extracted from the placenta with a fine needle) or amniocentesis (where fluid is extracted from the sac around the baby).
Anomaly scan
Offered to most women around 19-20 weeks, this is a detailed scan designed to detect any abnormalities in your baby. Your baby's head circumference and abdomen will be measured and her heart, brain and limbs will also be checked. Some hospitals will tell you the sex of your baby at this scan, while others have a policy not to reveal it.
After 20 weeks
You may be offered extra scans if you have a complication, such as placenta praevia. If there's a family history of birth defects, such as heart defects, you may also have later checks, or if you are expecting twins or triplets.
Should I have a scan?
Ultrasound scans are not compulsory and it's important to consider your reaction to what a scan may reveal. Most babies are fine, but you should be prepared for the fact that a scan could indicate a problem.
Are they safe?
There have been many studies comparing babies who have been scanned with those who haven't. No problems have appeared in all but one study and the current consensus is that ultrasound is safe. However, ultrasound should never be carried out lightly.
Could 3-D scans be the future?
A new ultrasound scanner, available at only a few hospitals and private clinics, lets you see a 3-D picture of your baby. Ask your doctor or midwife about facilities in your area."
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