Treatments and tests

Diagnostic tests for your baby during pregnancy

A diagnostic test is used to confirm a chromosomal condition, such as Down syndrome, or a genetic condition in the baby.

You may choose to have a diagnostic test if you have:

  • had a previous pregnancy with Down syndrome or other birth defect
  • been identified as at increased risk of having a baby with a genetic condition after a first or second trimester screening test
  • a family history of a genetic condition.

Types of diagnostic tests

Diagnostic tests used during pregnancy can be invasive or non-invasive and  include:

  • chorionic villus sampling
  • amniocentesis
  • ultrasound.

Invasive diagnostic tests

Both chorionic villus sampling and amniocentesis are very invasive and can increase the risk of pregnancy loss (miscarriage). The risk of pregnancy loss for both procedures, however, is less than 1 in 100 (less than 1 per cent). For this reason diagnostic tests are not routinely offered to all women but rather to those whose screening tests have identified an increased risk of Down syndrome.

Chorionic villus sampling

This test is done between weeks 11 to 14 of your pregnancy.

A needle, guided by ultrasound to avoid harming your developing baby, is inserted through your abdomen (stomach) or cervix to take a sample of chorionic villus cells from your placenta. This sample is tested for missing, extra or abnormal chromosomes.

The test is done as an outpatient procedure (you won’t need to be admitted to hospital) and takes about 20 minutes. You will be awake during the procedure. Many women find the diagnostic tests uncomfortable and this discomfort is often managed by local anaesthetic. It is suggested you rest for about 20 minutes after the procedure and take things easy for 1 to 2 days after the test.

The risk of pregnancy loss (miscarriage) from this procedure is less than 1 in 100 (less than 1 per cent).

Cross section of a pregnant woman’s abdomen with a needle being inserted through the top of abdomen to take a sample of placenta cells.

© Royal College of Obstetricians and Gynaecologists
Figure 1: Chorionic villus sampling through the abdomen

Cross section of a pregnant woman’s abdomen with a needle being inserted through the woman’s cervix to take a sample of placenta cells.

© Royal College of Obstetricians and Gynaecologists
Figure 2: Chorionic villus sampling through the cervix (entrance to the womb)

Amniocentesis

This test is done between weeks 15 to 18 of your pregnancy.

A needle, guided by ultrasound to avoid harming your developing baby, is inserted through your abdomen (stomach) to take a small sample of amniotic fluid (the fluid that surrounds the baby in the uterus).This sample is tested for missing, extra or abnormal chromosomes.

Amniocentesis is an outpatient procedure that takes about 20 minutes. You will be awake during the procedure. Many women find the diagnostic tests uncomfortable and this discomfort is often managed by local anaesthetic. It is suggested you rest for about 20 minutes after the procedure and take things easy for 1 to 2 days after the tests.

The risk of pregnancy loss (miscarriage) is less than 1 in 100 (less than 1 per cent).

Cross section showing a needle inserted through a pregnant woman's abdomen to sample the fluid near the baby.

© Royal College of Obstetricians and Gynaecologists
Figure 3: Amniocentesis

Results

The samples collected by chorionic villus sampling or amniocentesis are tested in a laboratory. Depending on the test, results may be available within 24 hours, but it may take up to 14 days.

Your doctor will explain the test result and, if relevant, how this affects you and your developing baby. If a genetic condition is found, genetic counselling with Genetic Services of Western Australia (external site) may be recommended.

If testing confirms your baby has Down syndrome, Trisomy 13 or Trisomy 18, your doctor or a genetic counsellor will be available to discuss your choices with you but will allow you to make the decision that is right for you. Your choices include ending the pregnancy, continuing the pregnancy, or placing the baby for adoption.

Limitations

Chorionic villus sampling and amniocentesis tests will detect practically all chromosomal abnormalities associated with Down syndrome, Trisomy 13 and Trisomy 18. A normal result means your baby does not have Down syndrome or other common chromosomal conditions, but it does not rule out all birth defects.

Costs

There may be costs for having the diagnostic tests. You may be able to claim part of this cost from Medicare. Please ask when you book your appointment, for the costs and any rebates available for the diagnostic tests.

Non-invasive diagnostic tests

Ultrasounds are not invasive so there no risk of harm to you or your baby. You may be offered an ultrasound to diagnose conditions such as cardiac problems in your baby.

Routine structural ultrasound

An ultrasound machine is used to provide images of your baby in your uterus (womb).

Find out more about ultrasound in pregnancy.

An 18 to 20 week ultrasound is recommended to check:

  • the position of the placenta
  • the amount of amniotic fluid (the fluid that surrounds the baby in the uterus)
  • the baby’s growth
  • for structural abnormalities such as in the heart, limbs, abdomen, bones, brain, spine and kidneys.

Understanding the results

Ultrasound results may be available immediately or may be sent to your doctor. If a physical abnormality is found your doctor will explain what this means and refer you to specialists where appropriate.

Limitations

The accuracy of the ultrasound depends on a number of factors, including:

  • the equipment used
  • your weight
  • the developmental stage of your baby
  • its position in your uterus
  • the visibility of the abnormality.

Costs

There may be a charge for having a routine structural ultrasound. You may be able to claim part of this cost from Medicare. When you book your appointment please ask for the costs and any rebates available.

More information

Remember

  • If your screening test results shows your baby is at increased risk you may wish to have diagnostic tests. Diagnostic tests confirm the presence of a condition and are very accurate.
  • Some diagnostic tests can increase the risk of pregnancy loss (miscarriage).
  • Screening and diagnostic tests during pregnancy cannot detect all health conditions.

Acknowledgements

Office of Population Health Genomics


This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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