This factsheet is for women who are having an ultrasound scan during pregnancy, or who would like information about the procedure.
Ultrasound can be used to monitor your baby's growth and check for physical abnormalities. It uses high-frequency sound waves and their echoes to create moving three-dimensional (3D) or four-dimensional (4D) images of your growing baby. The pictures (scans) are black, white and grey and are displayed on a screen.
You will meet the obstetrician or sonographer carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs. Details of the procedure may also vary from country to country.
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Published by Bupa's health information team, March 2010.
About ultrasound in pregnancyUltrasound scans in pregnancy are usually performed by an obstetrician or sonographer. Obstetricians are doctors specially trained in pregnancy and childbirth. Sonographers are technicians specially trained in taking ultrasound scans.
There are different reasons for doing ultrasound scans at different stages during pregnancy. In some countries, women are offered scans early in pregnancy to confirm the pregnancy and check when their baby will be due; and later in pregnancy to check that the baby is developing normally. Scans may also be offered to certain pregnant women because of their age and medical or family history.
First trimesterYou may be offered an ultrasound scan in the first 12 weeks of your pregnancy to confirm the pregnancy, check for a heartbeat and check when your baby is due. Knowing how many weeks old your developing baby is (the gestational age) can help doctors monitor important milestones during your pregnancy. A scan done at this time can also tell you if you're expecting more than one baby, and may be able to help to estimate the chance that your baby has Down's syndrome.
Second trimesterYou may be offered another scan to check your baby's development later on in your pregnancy. At this stage, your obstetrician or sonographer can check for abnormalities that can be seen with a scan. He or she may check your baby's heart, brain, kidneys, liver and spine, and measure the arms, legs and head.
Your sonographer will also be able to check the position of the placenta, which provides vital nutrients and oxygen-rich blood to your baby. If the placenta is lying unusually low in the womb, this is called placenta praevia. This often resolves before the baby is born, but if it doesn't, you may need to have a caesarean delivery (an operation to deliver your baby through your abdomen).
Other ultrasound scans in pregnancyYou may be offered more scans during pregnancy if your doctor or midwife thinks there may be a problem with your baby or the placenta. For example, if:
- a previous scan showed a low-lying placenta
- you have diabetes and are at risk of having a large baby
- your midwife thinks your baby may be in a breech position (bottom-down rather than head-down)
- your baby is smaller than it should be for your stage of pregnancy
- you have vaginal bleeding during pregnancy
Doppler ultrasoundOne type of ultrasound scan that is sometimes used is called Doppler ultrasound. This monitors flow in blood vessels and can be used to check placenta function. Problems with the placenta can affect your baby's growth and development. Doppler scans are only done if your obstetrician or midwife thinks there might be a problem with the placenta.
Fetal echocardiogramFetal echocardiogram is a type of Doppler ultrasound done by a specialist to examine your baby's heart before birth. It's usually done at around 18-24 weeks by scanning through your abdomen (tummy). It can also be done earlier in pregnancy through your vagina. You may be offered a fetal echocardiogram if a previous scan has shown abnormalities, or if your baby is at risk of having heart problems.