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Ultrasound scan

ultrasound; scan; ultra; sound; waves; placenta; multiple;

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What is ultrasound?

Ultrasound uses sound waves to create an image (picture).  The sound waves can not be heard and the power of the sound waves used is very low. In pregnancy an ultrasound scan can be used to look at the developing baby.

An ultrasound is safe for both mother and baby because it does not use ionising radiation (it is different to an x-ray).  To date, 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 their pregnancy.

Pregnancy is an exciting time for both parents, but there can be worries.  Talk to your doctor or midwife if there are any concerns or questions about your pregnancy and for more information before you decide whether or not to have a test done.

Ultrasound is a diagnostic test and is done for medical reasons only.

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Why is an ultrasound scan done?

There are many different medical uses for an ultrasound scan during pregnancy.
The most common ones are:

  • To determine viability of pregnancy (check if the baby is alive)
  • To check the number of babies present
  • To work out the age of baby in a dating scan
  • To check the baby's growth and physical development
  • To monitor the pregnancy if there have been  complications, such as bleeding, fluid loss, hypertension (high blood pressure) or gestational diabetes
  • To check the position of the placenta and assess amount of amniotic fluid around the baby
  • To monitor placental health and function.

Other reasons for an ultrasound scan

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, with signs of pregnancy being seen as early as 5 weeks. They are used to give different information at different times during the 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 and accredited 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 ½ hr to about 1 hour or more.

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 required at a later date.

If you wish, it may be possible to have a paper 'picture' of the baby for you to keep.

If you do not want to watch the screen, tell the sonographer 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 (water, juice, cordial or clear tea - not milky or fizzy drink) finishing half an hour before the scan. Do not empty your bladder before the ultrasound.

The scan can determine the viability of pregnancy, number of baby/babies, baby's age and to investigate possible reasons for vaginal bleeding and/or pain during pregnancy

Morphology scan – a look at your baby's body

This scan is best done from 19-20 weeks to fully assess baby.  It is a very detailed examination which usually takes about 45 minutes to 1 hour depending on your baby's position.

During this scan, the sonographer looks at the baby's head, face, spine, heart, abdomen, kidneys, arms and legs to ensure that they can be seen and are normal. (Some problems may not be picked up by this scan.)

Trans-vaginal ultrasound – through the vagina

In some cases, it is very difficult to assess baby through the abdomen due to bowel gas or the thickness of tissue under the skin.  Increased fatty tissue commonly makes it harder to see the baby clearly. An internal scan can be the best option to get a better look at baby.

In this procedure, women are asked to remove any piece of clothing from their waist down including their undergarments.  A firm wedge is then placed under the woman's bottom to raise the pelvis.  The transducer is a long tubular structure with a handle.  It is covered with a condom and sterile gel is put on the tip so that it can be placed into the vagina easily.  If you consent to this, the transducer is inserted into the vagina, which gives a clearer view of baby.

In most cases, some pressure is applied on a patient's abdomen and transducer to move overlying bowel gas.  It is important to let the sonographer know if you feel any pain.  This procedure is uncomfortable but should not be painful

Trans-vaginal scan are commonly done in early pregnancies for dating scans.

What can an ultrasound tell about a baby?

Ultrasound scans 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 anxiety. Your doctor or midwife can provide more information and support.

Ultrasound can usually show the baby's gender, but it is not always 100% guaranteed. 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 'Screening tests for Down syndrome'.

An ultrasound cannot detect all problems a baby may have. Having a normal result on an ultrasound scan does not guarantee that your baby will not have a birth defect or chromosomal abnormally.

Information in this topic comes from the Perinatal Ultrasound Department of the Women's and Children's Hospital (South Australia) October 2011.

South Australia
Maternal Fetal Medicine Unit

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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.

 

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