Amniocentesis is a test you may be offered during pregnancy to check if your baby has a genetic or chromosomal condition, such as Down's, Edwards' or Patau's syndrome.
It involves removing and testing a small sample of cells from the amniotic fluid – the fluid that surrounds the unborn baby in the womb (uterus).
Amniocentesis isn't offered to all pregnant women – only if there's a higher chance your baby could have a genetic condition.
This could be because:
It's important to remember that you don't have to have amniocentesis if it's offered. It's up to you to decide whether you want it.
Your midwife or doctor will speak to you about what the test involves, and let you know what the possible benefits and risks are, to help you make a decision.
Read more about why amniocentesis is offered and deciding whether to have it.
Amniocentesis is usually carried out between the 15th and 20th weeks of pregnancy but may be later if necessary.
It can be performed earlier, but this may increase the risk of complications of amniocentesis and is usually avoided.
During the test, a long, thin needle is inserted through your abdominal wall, guided by an ultrasound image. The needle is passed into the amniotic sac that surrounds the foetus and a small sample of amniotic fluid is removed for analysis.
The test itself usually takes about 10 minutes, although the whole consultation may take about 30 minutes.
Amniocentesis is usually described as being uncomfortable rather than painful. Some women describe experiencing a pain similar to period pain or feeling pressure when the needle is taken out.
Read more about what happens during amniocentesis.
The first results of the test should be available within three working days and will tell you whether Down's, Edwards' or Patau's syndrome has been discovered.
If rarer conditions are also being tested for, it can take three weeks or more for the results to come back.
If your test shows that your baby has a genetic or chromosomal condition, the implications will be fully discussed with you. There's no cure for most of the conditions amniocentesis finds, so you'll need to consider your options carefully.
You may choose to continue with your pregnancy, while gathering information about the condition so you're fully prepared, or you may consider having a termination (abortion).
Read more about the results of amniocentesis.
Before you decide to have amniocentesis, the risks and possible complications will be discussed with you.
One of the main risks associated with amniocentesis is miscarriage, which is the loss of the pregnancy in the first 23 weeks. This is estimated to occur in 0.5-1% of women who have amniocentesis.
There are also some other risks, such as infection or needing to have the procedure again because it wasn't possible to accurately test the first sample.
The risk of amniocentesis causing complications is higher if it's carried out before the 15th week of pregnancy, which is why the test is only done after this point.
Read more about the possible complications of amniocentesis.
An alternative to amniocentesis is a test called chorionic villus sampling (CVS). This is where a small sample of cells from the placenta (the organ that links the mother's blood supply with her unborn baby's) is removed for testing.
It's usually carried out between the 11th and 14th weeks of pregnancy, although it can be performed later than this if necessary.
With CVS, the risk of miscarriage is similar to the risk of miscarriage for amniocentesis. However, as the test can be carried out earlier, you'll have more time to consider the results.
If you're offered tests to look for a genetic or chromosomal condition in your baby, a specialist involved in carrying out the test will be able to discuss the different options with you and help you make a decision.
Amniocentesis is only offered to pregnant women who have a higher chance of having a baby with a genetic or chromosomal condition. It can diagnose a range of conditions.
If your test results, or medical or family history suggest you have a higher chance of having a baby with a genetic or chromosomal condition, you may be offered amniocentesis.
You don't have to take the test – it's up to you to decide whether you want it.
Amniocentesis can be used to diagnose a number of conditions, including:
If you're offered amniocentesis, ask your doctor or midwife what the procedure involves, and what the risks and benefits are before deciding whether to have it.
You may also find it helpful to contact a support group, such as Antenatal Results and Choices (ARC), a charity that offers information, advice and support on all issues related to screening during pregnancy.
It will usually be able to tell you whether your baby will be born with any of the conditions tested for.
If no problem is found, it may be reassuring, while a result showing that a condition was detected will give you plenty of time to decide how you want to proceed with your pregnancy. Read about the results of amniocentesis for more information.
There's a 0.5-1% chance you could have a miscarriage after the procedure. You may feel this outweighs the potential benefits of the test. Read more about the risks of amniocentesis.
Some women decide they would rather find out when their baby is born.
Amniocentesis involves taking a small sample of amniotic fluid so the cells it contains can be tested. Amniotic fluid surrounds the unborn baby (foetus) in the womb (uterus).
You won't usually need to do anything special to prepare for amniocentesis. You can eat and drink as normal beforehand.
In some cases, you may be advised to avoid going to the toilet for a few hours before the test because it's sometimes easier when your bladder is full. Your doctor or midwife will tell you about this before you attend your appointment.
You may want to bring a partner, friend or family member for support when you have the test.
You'll have an ultrasound scan before and during amniocentesis. An ultrasound scan uses high-frequency sound waves to produce an image of your womb that's relayed to a monitor.
The ultrasound scan allows healthcare professionals to:
Before the needle is inserted into your abdomen, the area may be numbed with anaesthetic. This involves having a small injection into your belly and may sting slightly.
However, anaesthetic isn't usually necessary because research suggests it doesn't have much effect in most cases.
An antiseptic solution will first be used to clean your abdomen to minimise the risk of infection. A long, thin needle is then inserted through your abdominal wall. It may cause a sharp stinging sensation.
Using the ultrasound image as a guide, the needle is passed into the amniotic sac that surrounds the baby. A syringe is then used to remove a small sample of the amniotic fluid, which will be sent to a laboratory for analysis.
In about 8 out of every 100 women who have amniocentesis, not enough fluid is removed the first time the needle is inserted. If this happens, the needle will be inserted again.
Amniocentesis isn't usually painful, but you may feel uncomfortable during the procedure.
Some women describe experiencing a pain similar to period pain, or feeling pressure when the needle is taken out.
The procedure usually takes around 10 minutes.
Afterwards, you will be monitored for up to an hour in case the test causes any side effects, such as heavy bleeding. You can then go home to rest.
It's a good idea to arrange for someone to drive you home, as you might not feel up to it yourself.
After amniocentesis, it's normal to have cramps similar to period pain and light vaginal bleeding called "spotting" for a day or two.
You can take over-the-counter painkillers such as paracetamol – but not ibuprofen or aspirin – if you experience any discomfort.
You may wish to avoid any strenuous activity for the rest of the day.
Contact your midwife or the hospital where the procedure was carried out for advice as soon as possible if you develop any of the following symptoms after the procedure:
The first results should be available within a few days, and this will tell you if a genetic or chromosomal condition has been discovered.
You can usually choose whether to get the results over the phone, or during a face-to-face meeting at the hospital or at home.
After amniocentesis has been carried out, the sample of amniotic fluid will be sent to a laboratory for testing.
The first results should be available within three working days, and this will tell you whether a chromosomal condition such as Down's syndrome, Edwards' syndrome or Patau's syndrome has been found.
You can usually choose whether to get the results over the phone, or during a face-to-face meeting at the hospital or at home. You'll also receive written confirmation of the results.
Amniocentesis is estimated to give a definitive result in 98-99% of cases.
However, it can't test for every birth defect and, in a small number of cases, it's not possible to get a conclusive result.
For many women who have amniocentesis, the results of the procedure will be "normal". This means that none of the conditions that were tested for were found in the baby.
However, a normal result doesn't guarantee that your baby will be completely healthy as the test only checks for conditions caused by faulty genes, and it can't exclude every condition.
If your test is "positive", your baby has one of the conditions they were tested for. In this instance, the implications will be fully discussed with you and you'll need to decide how to proceed.
If the test finds that your baby will be born with a condition, you can speak to a number of specialists about what this means.
These could include your midwife, a consultant paediatrician, a geneticist and/or a genetic counsellor.
They'll be able to give you detailed information about the condition – including the possible symptoms your child may have, the treatment and support they might need, and whether their life expectancy will be affected – to help you decide what to do.
A baby born with one of these conditions will always have the condition, so you'll need to consider your options carefully. Your main options are:
This can be a very difficult decision, but you don't have to make it on your own.
As well as discussing it with specialist healthcare professionals, talk things over with your partner and speak to close friends and family, if you think it might help.
The charities Antenatal Results and Choices (ARC), Down's Syndrome Association, Sickle Cell Society and SOFT (Support Organisation for Trisomy 13 and 18) can also offer support and information.
Before you decide to have amniocentesis, you'll be told about the risks and possible complications.
The main risks associated with the procedure are outlined below.
There's a small risk of miscarriage (loss of the pregnancy) occurring in any pregnancy, regardless of whether or not you have amniocentesis.
If you have amniocentesis after 15 weeks of pregnancy, the chance of having a miscarriage is estimated to be 0.5-1%. The risk is higher if the procedure is carried out before 15 weeks.
It's not known for certain why amniocentesis can lead to a miscarriage. However, it may be caused by factors such as infection, bleeding or damage to the amniotic sac that surrounds the baby.
Most miscarriages that happen after amniocentesis occur within three days of the procedure. However, in some cases, it can occur up to two weeks later. There's no evidence that you can do anything during this time to reduce your risk.
During amniocentesis, the placenta (the organ that links the mother's blood supply to her unborn baby's) may be punctured by the needle.
It's sometimes necessary for the needle to enter the placenta to access the amniotic fluid. If this happens, the puncture wound usually heals without any more problems developing.
An ultrasound scanner is used to guide the needle, significantly reducing the risk of injury.
As with all surgical procedures, there's a risk of infection during or after amniocentesis. However, the rate of severe infection for amniocentesis is lower than 1 in 1,000.
If your blood type is rhesus (RhD) negative but your baby's blood type is RhD positive, it's possible for "sensitisation" to occur during amniocentesis.
This is where some of your baby's blood enters your bloodstream and your body starts to produce antibodies to attack it. If it's not treated, this can cause the baby to develop rhesus disease.
If you don't already know your blood type, a blood test will be carried out before amniocentesis to see if there's a risk of sensitisation. An injection of a medication called anti-D immunoglobulin can be given to stop sensitisation occurring.
Read more about preventing rhesus disease.
Having amniocentesis early (before week 15 of the pregnancy) has been associated with an increased risk of the unborn baby developing club foot.
Club foot, also known as talipes, is a congenital (present at birth) deformity of the ankle and foot.
Because of the increased risk of a baby developing club foot, amniocentesis isn't recommended before 15 weeks of pregnancy.
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