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What Is Amniocentesis?

Amniocentesis is a test usually carried out to examine a baby’s chromosomes, most commonly in search for Down’s Syndrome. Amniocentesis is always voluntary and parents decide if they wish to choose to have this test. The information below may help you to decide whether or not to have this test.

Amniocentesis is the withdrawal of a small amount of fluid from around the baby (amniotic fluid). Cells from the baby’s skin and bladder are in the fluid and can be grown in the laboratory for chromosome analysis. Chromosomes are tiny microscopic packages present in every cell of the body. Normally in each human cell there are 46 chromosomes. A missing or extra chromosome causes many changes in the way an unborn baby develops. Amniocentesis can detect Down’s Syndrome (which is caused by an extra no.21 chromosome), other chromosome abnormalities and certain genetic conditions, when there is a family history of such a disease

How is amniocentesis performed?

Amniocentesis is generally performed from 15 weeks gestation up to the date the baby is due. An ultrasound scan will be done first to check the position of the baby/placenta and to find a pocket of amniotic fluid. The skin on the mother’s abdomen (tummy) is cleaned with anti-septic fluid and a very fine needle is passed through the abdomen and into the womb. A small amount of fluid around the baby (amniotic fluid) is withdrawn. The needle is carefully watched with the ultrasound scan to ensure that it is in the correct position. The test lasts for 2-3 minutes and afterwards the baby’s heartbeat is checked. Local anaesthetic is not usually used as the insertion of the anaesthetic is often more uncomfortable than the test itself. Occasionally it may be necessary to pass the needle into the abdomen a second time. If your blood group is Rhesus negative you will require an injection of Anti-D to prevent blood incompatibility developing between you and the baby as a result of the amniocentesis test.

What should I expect after amniocentesis?

For the first few days you may experience some abdominal discomfort, period like pain or a little bleeding. These are relatively common and in the vast majority of cases, the pregnancy continues without a problem. You may find it helpful to take some simple pain relief like paracetamol (this is safe in pregnancy) and rest for a few hours.

When can I expect to get the results?

Results of the test are usually available in 2-3 weeks, this is because the cells have to grow before they can be examined. After the amniocentesis arrangements will be made to contact you with the results as soon as they are obtained from the National Genetics Centre Our Lady’s Hospital, Crumlin.

Most people are happy to receive the results over the phone but if you wish to come and obtain the result in person this can be organised. The full result will also tell whether you are expecting a boy or girl – so you may want to give some thought whilst awaiting the result as to whether or not you would like to have this information.

What are the risks associated with amniocentesis?

One in one hundred women who have an amniocentesis test will experience a miscarriage. There are no ways of predicting who will miscarry.

For Down’s Syndrome the amniocentesis result will clearly state whether the baby is affected or not, with a high degree of accuracy (99%).


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Video Transcript
Video title: Amniocentesis-What Is Amniocentesis

An amniocentesis is a test which we undertake to determine whether the baby has a chromosomal abnormality. This includes conditions such as Down’s syndrome. The Test itself is undertaken at or beyond fifteen weeks to suit the needs or a mum’s request and often follows on from a screening test such as a nuchal translucency first trimester biochemistry test.

The test itself involves placing a very fine needle through the tummy wall and drawing off some fluid from around the baby. We culture the cells that are in this fluid in order to determine exactly what the baby’s chromosome make up is. Most patients tolerate this test very well, but unfortunately about 1% of patients experience a miscarriage following an amniocentesis.
The results of this test take about two to three weeks to come back. Patients are offered to have this result imparted to them over the phone or in a face to face consultation.

It is very important that you give great consideration as to whether to have this test or not, because of the risk of miscarriage and also as to what you’re going to do with the information.

Patients can be referred either by their GP or their obstetrician to have this test undertaken, but if you have any concerns and you wish to discuss it, please call.