Ultrasound scan
ultrasound; scan; ultra; sound; waves; placenta; multiple;
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Ultrasound uses sound waves to make an image (picture). In pregnancy an ultrasound scan can be used to make an image of the developing baby.
An ultrasound is painless for the mother and the baby. The sound waves cannot be heard and the power of the sound waves is very low. Ultrasound does not involve radiation. No evidence has been found of ultrasound causing any harm to either the mother or developing baby. In most developed countries about 90% of women have at least one ultrasound during pregnancy.
There are many things to think about before deciding whether or not to have a test in pregnancy. Talk with your doctor or midwife about issues, questions or concerns that you have.
Why is an ultrasound scan done?
There are many different medical uses for an ultrasound scan in pregnancy.
The most common are:
- To check how far along the pregnancy is.
- To see if there is more than one baby.
- To check the baby's growth and physical development.
- To check the pregnancy if there has been a complication, such as bleeding.
- To check the position of the placenta and amount of fluid around the baby (amniotic fluid).
Other reasons for doing an ultrasound scan
- For nuchal translucency screening to see if the baby is at an increased risk of having a chromosomal problem (have a look at the topic Screening tests for Down syndrome).
- To check the development of the baby's brain and spine if there is an increased risk that the baby has spina bifida (have a look at the topic Screening tests for neural tube defects).
- To get a clear image of the baby when a test such as Chorionic Villus Sampling (CVS) or amniocentesis are being done. (For more information have a look at the topics about these tests.)
Ultrasounds are done for medical reasons only.
When is an ultrasound scan done?
The most common time for a scan is about 19-20 weeks of pregnancy. This is the best time to check the baby's physical development.
Ultrasound scans can be done at any stage of pregnancy after the first 6 weeks. They are used to give different information at different times in the pregnancy.
Most women will have at least one scan in pregnancy.
How is an ultrasound done?
Ultrasound is an outpatient procedure (you will not be admitted to hospital), and it is done by a specially trained sonographer or doctor.
During the ultrasound, sound waves are sent either through the woman's abdomen or through the vagina – the person doing the scan will discuss which option is best for you. The length of the scan will depend on the reason for the scan and can take from several minutes to about ¾ hour.
Your partner or a support person will usually be able to be with you during the scan.
Sometimes, due to the position of the baby, good views cannot be obtained and a repeat scan is needed at a later date.
If you wish it may be possible to have a paper 'picture' of the baby, or even a short video.
If you do not want to watch the screen, tell the person doing the scan before the scan starts.
Early pregnancy
For ultrasounds early in pregnancy the best views are obtained if the woman's bladder is full. The uterus is often hidden behind the bowel making it difficult to see. When the bladder is full the bowel is pushed out of the way.
Starting about an hour before the appointment time you will need to drink about 500ml of clear fluid (not milky or fizzy drink) finishing half an hour before the scan. Do not empty your bladder before the ultrasound.
Abdominal ultrasound
A jelly-like substance will be put onto the skin of the abdomen. An instrument like a microphone (called a transducer) is then pushed against the skin. Sound waves pass from the transducer into the uterus and through the fluid around the baby. The sound waves bounce harmlessly off the baby, creating echoes.
A computer changes these echoes into a picture on a monitor (like a television screen).
Vaginal ultrasound
Vaginal ultrasound is very similar to abdominal ultrasound, but instead of the transducer being pressed against the skin of the abdomen a transducer with a sterile cover is placed into the woman's vagina.
Vaginal ultrasound may be used if good views cannot be obtained by abdominal ultrasound. It is rare for this to be needed at the 19 week scan.
What can an ultrasound tell about a baby?
Ultrasound cannot detect all problems with a baby. Ultrasound can detect some types of physical birth defects.
Examples of physical birth defects that may be found at 19 - 20 weeks are most cases of spina bifida, some serious heart defects, some kidney problems, absence of part of a limb and some cases of cleft palate.
Sometimes ultrasound will show things of minor or uncertain significance but it may not be possible to tell during pregnancy whether this means the baby has a problem. This uncertainty or 'not knowing' may cause you to worry. Your doctor or midwife can provide support.
Ultrasound can sometimes show what sex the baby is, but it is not always right. You may choose whether or not you wish to be told.
The results will be sent to the doctor who referred you to have the scan.
What if the ultrasound shows that a baby has a problem?
If the ultrasound shows that the baby has a problem, a medical specialist will talk with you about what this is likely to mean for the baby.
Other tests may be needed to get more information. These tests may include a further scan at a later date or a test to examine the baby's chromosomes (have a look at the topic 'Screening tests for Down syndrome').
An ultrasound cannot detect all problems with a baby. Having a normal result on an ultrasound scan does not guarantee that your baby will not have a birth defect.
Information in this topic comes from the brochure 'Ultrasound' published by the Women's and Children's Hospital (South Australia) 2003.
The information on this site should not be used as an alternative to professional care. If you have a particular problem, see your doctor or midwife.