Amniocentesis

You will experience the amniocentesis test during the second trimester of your pregnancy, between 16 and 20 weeks.  

What is an amniocentesis?

An amniocentesis is a diagnostic test that is performed in pregnancy to determine if an unborn baby has a chromosomal condition. It is a test that can be offered to pregnant women after a “high risk” screening result. It is usually done between 15 and 20 weeks of pregnancy, or later if required.

Amniocentesis involves extracting fluid from your baby’s amniotic sac. Cells are then extracted and grown in a laboratory and tested for chromosomal abnormalities. Amniocentesis is a diagnostic test, this means that it will be able to give you a definitive result of if your baby has a chromosomal condition.

How is amniocentesis performed?

An amniocentesis is is done by inserting a needle through your abdomen, under local anaesthetic by an obstetrician. The needle is then passed into the amniotic sac that surrounds your unborn baby and a small sample of amniotic fluid is removed and tested.  Ultrasound is used to guide the needle and reduce the risk of baby being harmed.

The actual amniocentesis takes about 10 minutes and women report that it feels uncomfortable rather than painful.

Prior to the test, a specialist midwife or doctor will talk you through what is involved in this test and let you know the benefits, risks, alternatives and what happens if you do nothing.

Why would I have the amniocentesis test?

Amniocentesis is not offered to all pregnant women, but only to those where there is a higher chance your baby could have a genetic condition. This could be because your pregnancy screening results have come back to suggest a ‘high risk’, or you have had a previous pregnancy with a chromosomal condition, or you have a family history of a genetic condition such as cystic fibrosis.

What are the risks of amniocentesis?

There is a 1% risk of miscarriage. You’ll have an ultrasound scan before and during the procedure to reduce this risk. The risk of miscarriage is higher if performed before the 15th week of pregnancy, which is why amniocentesis is done after this point in pregnancy.

There is a small risk of infection, with a rate of infection after amniocentesis being less than 1 in 1,000.

It’s common to experience some cramping pains for 24 hours after an amniocentesis, but if you experience bleeding, fluid loss from your vagina or signs of infection, you should contact your healthcare provider.

The results of the amniocentesis test

The first set of results come back within 3 days. These give a diagnosis within three days for Down's syndrome, Edward’s syndrome and Pateau’s syndrome.

More detailed results, which check for any other, rarer, changes in the baby's chromosomes may take up to three weeks.

If you have received your results that show that baby has been diagnosed with a chromosomal condition, the implications of this condition will be fully discussed with you and you will be given as much time as you need to consider your options.

Your options will be to continue with the pregnancy with the full support of your specialist team. You will be given lots of information and support to prepare you on what to expect.

Or, you will be given the option to terminate your pregnancy, again with the full support of your team.

There is a charity called ARC opens in a new tab/window where you can find further support, counselling & unbiased information on antenatal screening, the results & your choices.

Are there any alternatives to amniocentesis?

An alternative to amniocentesis is a test calledv choronic villus sampling (CVS); this is where a small sample of cells from the placenta is removed and tested. This can be done slightly earlier than the amniocentesis, between 11 & 14 weeks of pregnancy.

Another alternative is to do nothing. It’s important to keep in mind that you do not have to have this test, it's completely your choice. You should be fully counselled about all your options prior to having the procedure.