What is amniocentesis?
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Amniocentesis is a prenatal diagnostic test performed at around 16 weeks of pregnancy. It is used to test for chromosomal abnormalities such as Down syndrome. It involves passing a needle through the skin of the mother, through the wall of the uterus (womb) and taking a small sample (around 16mls) of the fluid surrounding the developing baby. The needle does not touch the baby or the placenta.
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The cells in the fluid can be used to investigate the baby's chromosomes; which is why it is possible to find out from this investigation if the baby has Down syndrome, or any of the other chromosome disorders. The test can also determine the baby’s sex.
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Who is offered amniocentesis?
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- Women who are 37 years and over at the estimated time of delivery. This is because as the age of the woman increases the chance of her having a baby with a chromosomal abnormality also increases.
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- Women who have had a prenatal screening test (such as first trimester screening, maternal serum screening or ultrasound) that has shown an increased risk for birth defect.
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- Women who have already had a child with a problem such as Down syndrome.
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- Women who are known to have a pregnancy at risk of an hereditary condition that might be passed on to their baby.
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What will happen on the day of the test?
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You will have an ultrasound scan to check that there is only one baby and that the pregnancy appears normal. The scan will also confirm the age of the baby and position of the placenta. (For more information about ultrasound see the ultrasound fact sheet).
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The skin on your abdomen will be cleaned and a thin needle inserted into your uterus. The doctor will use the ultrasound screen to guide the needle. It only takes about 30-45 seconds to draw up the 16mls of fluid required into the syringe.
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After the needle is removed and the baby is checked again, you will be able to leave the room. You will need to sit quietly for 30 minutes or so and then you can go home.
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Almost without exception women tell us that they experience far less discomfort than they expect and that the discomfort is usually very minor.
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You will be quite capable of driving yourself home after the test, but if it is possible, it would be good to have someone accompany you and drive you home afterwards. We normally recommend that you take it quietly for the rest of the day and possibly the next day as well although there is no reason to go to bed.
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What complications can occur?
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The risk of miscarriage after an amniocentesis is not yet certain.
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Our own findings (at the Women’s) show that the miscarriage rate amongst women who have had an amniocentesis is no higher than those who have not had the test done (an estimated to be 1 in 200.)
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Apart from this very slight risk of a miscarriage the amniocentesis test does not appear to be associated with any other complications to the baby or to the pregnancy.
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Apart from this very slight risk of a miscarriage the amniocentesis test does not appear to be associated with any other complications to the baby or to the pregnancy.
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Rarely, the test may fail either because no specimen is obtained or because the laboratory cannot produce a result. In this instance you may be offered a repeat procedure.
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What should I look for after the test?
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After the test, it is very rare to have any problems at all. Occasionally there may be some mild discomfort due to a little bruising under the skin. If there is any loss of blood or water from the vagina or any other pains after the amniocentesis you should contact either the Emergency Department on (03) 9344 2301 or your own doctor.
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How long will the results take?
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The chromosome test takes two weeks because of the requirement to grow the cells in the laboratory and for the test to be analysed. The laboratory will send the results directly to your doctor.
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Summary
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Amniocentesis has very few complications. However, it is only performed on patients in special situations, the most common being because the mother is aged 37 years or over. The test will check for Down syndrome and other chromosome abnormalities. It is important to realise that while the combination of the ultrasound scan and amniocentesis goes along way to ensuring the baby is normal, it does not guarantee that every abnormality has been excluded.
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Disclaimer
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The Royal Women’s Hospital does not accept any liability to any person for the information or advice (or use of such information or advice) which is provided in this fact sheet or incorporated into it by reference. We provide this information on the understanding that all persons accessing it take responsibility for assessing its relevance and accuracy. Women are encouraged to discuss their health needs with a health practitioner. If you have concerns about your health, you should seek advice from your health care provider or if you require urgent care you should go to the nearest Emergency Dept.
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 This fact sheet is also available to download as PDFs in: Arabic, Chinese, Croatian, Khmer, Serbian, Tigrinian, Turkish, Vietnamese
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Last reviewed Jan 2008
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