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Women and Newborn Health Service

Health A – Z


King Edward Memorial Hospital

Amniocentesis - Fetal Monitoring

Amniocentesis is a prenatal diagnostic test offered between 15 -18 weeks of pregnancy to exclude or confirm the presence of chromosomal abnormalities such as Down syndrome or hereditary conditions such as Duchenne muscular dystrophy and skeletal dysplasia. Amniocentesis involves taking a small sample of the fluid surrounding the fetus that contains cells from the fetus which can then be tested in a laboratory. The results from such tests are 99% accurate for the specific test performed.

Further information and additional resources can be obtained from the Maternal Fetal Medicine Service.

What do the Results Mean?

Why is Amniocentesis Performed?

  1. A prenatal screening test (such as first trimester screening, maternal serum screening or ultrasound) has indicated increased risk for birth defect.
  2. You or someone in your family or partner's family has a hereditary condition that might be passed on to your children.
  3. You are 37 years or older.

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How is Amniocentesis Performed?

  • This is an outpatient test which takes 15 -30 minutes.
  • The bladder should be reasonably full to gain a clear ultrasound picture to guide the procedure.
  • A thin hollow needle is guided through the woman's abdomen into the uterus to obtain a small sample of amniotic fluid which is sent to a laboratory for testing.

Please click to view the MPEG video that shows ultrasound images during amniocentesis. It is 971KB in size and will take approximately 3 minutes to download using a 56K modem.

Following is a diagram of the amniocentesis procedure.

Diagram of the Amniocentesis Procedure

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Will There be any Pain or Discomfort?

Discomfort such as pressure, menstrual cramp and a little pain like a blood test has been described. There may be tenderness where the needle was inserted. It is recommended that you rest for a few minutes after the procedure and take things easy for several days but bed rest is not required.

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What are the Risks?

The risk of fetal loss is 0.5 - 1% as a result of amniocentesis under ultrasound guidance. That means there are between 1 and 2 chances of miscarriage for every 200 amniocentesis tests done. If there is any abdominal pain, or loss of blood or fluid from the vagina following the procedure, your doctor should be consulted. There is not considered to be any risk to the fetus from the needle when the procedure is guided by ultrasound.

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What do the Results Mean?

Results take up to two weeks for the cells to be grown in the laboratory and the test to be analysed. A negative result excludes ONLY the condition for which the test was performed. This does not guarantee the absence of other different birth defect/s. There is NO test to exclude all pregnancy abnormalities.

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