What is amniocentesis?
Amniocentesis is a test carried out during pregnancy which involves using a fine needle to remove a small amount of the amniotic fluid around your unborn baby (nothing but baby’s urine).
Amniocentesis is used to detect chromosomal abnormalities such as Down syndrome. It can also detect certain other genetic conditions, such as sickle cell disease or thalassaemia major.
Amniocentesis is known as a diagnostic test because it gives you a diagnosis. For example, it tells you that your baby does or does not have Down syndrome.
When should the test be carried out?
If you choose to have an amniocentesis, it will usually be carried out between the 16th and 20th week of your pregnancy. However, the test can be carried out later in pregnancy.
Why am I offered the test?
We will offer you an amniocentesis if you have received a HIGH- RISK (Screen Positive) from a screening test for Down syndrome.
You may also be offered a test if:
- doctor thinks you or your baby’s father may have a higher risk of passing on an inherited abnormality to your baby, for example sickle cell disease or thalassaemia major
- you have had a previous pregnancy where your baby was born with a genetic or chromosomal abnormality
- You or people in your family have been born with abnormalities
- You will also be offered this test if your scan has shown that your baby has an increased chance of having a chromosomal or genetic disorder.
Not all women are offered this test.
How do I decide whether I want to have the test?
It can be difficult to make a decision about having an invasive test. You may find it helpful to talk to your doctor, your friends and family. You may also find it helpful to talk to an emotional counselor at BFMC.
You should remember that only you can decide whether or not you want to have this test.
Is there a risk to my pregnancy if I have the test?
An invasive test may increase the risk of you having a miscarriage.
The overall risk of you having a miscarriage after amniocentesis is about 1:300(BFMC outcomes data base). In other words, about one in every 300 women who have an amniocentesis will miscarry.
Can I do anything to prevent a miscarriage after I have had amniocentesis?
There is nothing you can do to prevent a miscarriage after an amniocentesis. You do not need to rest in bed.
It is also hard to tell when you are most likely to miscarry after you have had an amniocentesis. Most miscarriages happen up to two weeks after the test while the risk may last for a total of 4 weeks. Some miscarriages, due to a pregnancy complication, not related to an invasive test will happen anyway, whether the test is done or not, especially when they happen a month after the procedure.
Other screening test results your doctor might need to know about
If your blood group is rhesus negative you will be offered an anti-D injection after the procedure. Your doctor will discuss this with you.
Because amniocentesis is an invasive test, we would want to know whether or not you have HIV or Hepatitis B.
Eating and drinking
It is safe to eat and drink as normal before and after the test.
How is the amniocentesis done?
An hour before the test, you will receive a test dose followed by a full dose of an antibiotic (One dose only) to cover infections.
Immediately before the test, your abdomen is cleaned to make sure that the test can take place in the most sterile conditions possible.
During the amniocentesis you will have an ultrasound scan to check the position of your baby. A fine needle is then inserted through your skin, through your abdomen and into your womb. The needle is used to remove a small sample (25ml) of the amniotic fluid surrounding your baby. Because the needle is so fine, local anaesthetic is not usually used.
Is an amniocentesis painful?
Most women say that having an amniocentesis is uncomfortable rather than painful like a period pain. You may notice some cramping for a few hours afterwards. This is normal. You can take paracetamol for any discomfort. If you experience any unusual symptoms immediately after the test or over the next few days for example, feeling shivery or feverish, have started leaking fluid or bleeding or have contractions, you should call us or your doctor (or both) straight away.
What happens after the amniocentesis?
After the test, the sample of amniotic fluid will be taken by you to the Genetics laboratory, Manipal Hospital for testing. Two types of laboratory test are used to look at your baby’s chromosomes – ‘PCR’ (polymerase chain reaction) and a ‘full karyotype’.
PCR checks for the three most common chromosomal abnormalities. These are Down syndrome (trisomy 21), Edwards’ syndrome (trisomy 18) and Patau’s syndrome (trisomy 13).The results from PCR laboratory tests are usually ready after three working days.
A full karyotype checks all your baby’s chromosomes. Results from this test are usually ready within two to three weeks. As the full karyotype test is more detailed, it can sometimes take more time to get the results.
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Clinical Background and Genetics
The main indication for prenatal chromosome analysis is a pregnancy that has been identified as being at risk of a chromosomal disorder. This risk may have been identified by:
Antenatal Down syndrome screening
Abnormalities Detected on ultrasound scan
A previous chromosome abnormality
Parent known to carry a chromosome abnormality