Amniocentesis

Amniocentesis is a test you may be offered during pregnancy to check if your baby has a genetic disorder, such as Down's syndrome.

It involves removing and testing a small sample of cells from amniotic fluid, which surrounds the foetus in the womb (uterus).

When amniocentesis is offered

Amniocentesis isn't routinely offered to all pregnant women. It's only offered if there's a high risk your baby could have a genetic condition.

This could be because:

• an earlier antenatal screening test has suggested there may be a problem, such as Down's syndrome, spina bifida or sickle cell anaemia
• you've had a previous pregnancy with these problems
• you have a family history of a genetic condition, such as cystic fibrosis or muscular dystrophy, and an abnormality is detected in your baby during a routine ultrasound scan

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.

How amniocentesis is performed

Amniocentesis is usually carried out between the 15th and 20th weeks of pregnancy, but may be performed later than this if necessary.

Although it can be performed earlier, 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.

Getting your results

The first results of the test should be available within three working days and this will tell you whether Down's, Edward's or Patau's syndrome has been discovered.

If rarer conditions are also being tested for, it can take two to three weeks or more for the results to come back.

If your test shows that your baby has a serious inherited or genetic disorder, 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.

What are the risks 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 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 that was removed.

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 carried out after this point.

Read more about the possible complications of amniocentesis.

What are the alternatives?

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) are 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 about 1-2%, which is slightly higher than 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 disorder 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 offered to pregnant women at risk of having a baby with a serious genetic disorder. It will diagnose any problems at an early stage.

Amniocentesis isn't routinely offered to all women during pregnancy. It's offered if your test results or medical or family history suggest you have an increased chance of having a baby with a genetic disorder.

You don't have to have the test if it's offered – it's up to you to decide whether you want it.

What conditions can amniocentesis detect?

Amniocentesis can be used to diagnose a number of serious genetic disorders, including:

• Down's syndrome –  a condition that typically causes some level of learning disability and a characteristic range of physical features
• Edward's syndrome and Patau's syndrome – conditions that can result in miscarriage, stillbirth or (in babies that survive) severe physical problems and learning disabilities
• cystic fibrosis – a condition in which the lungs and digestive system become clogged with thick, sticky mucus
• muscular dystrophy – a condition that causes progressive muscle weakness and disability
• sickle cell anaemia – where the red blood cells develop abnormally and are unable to carry oxygen around the body properly
• thalassaemia – a condition that affects the red blood cells, which can cause anaemia, restricted growth and organ damage

Amniocentesis can also test for neural tube defects. The most common neural tube defect is spina bifida, which can cause learning difficulties and paralysis (weakness) of the lower limbs.

Deciding whether to have amniocentesis

If you're offered CVS, 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). ARC is a charity that offers information, advice and support on all issues related to screening during pregnancy.

Reasons to have amniocentesis

The test will usually tell you whether your baby will be born with any of the genetic conditions that were tested for.

If no problem is found, it may be reassuring. A result showing that a genetic 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.

Reasons not to have amniocentesis

There is a 1% chance you could have a miscarriage after the procedure. You may feel this risk 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 foetus (unborn baby) in the womb (uterus).

Preparing for amniocentesis

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 to perform 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.

Ultrasound scan

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:

• check the position of the foetus
• find the best place to remove some amniotic fluid
• ensure the needle can pass safely through the walls of your abdomen (belly) and womb

Anaesthetic

Before the needle is inserted into your abdomen, the area may be numbed with anaesthetic. This involves having a small injection into your belly that may sting slightly.

However, anaesthetic isn't usually necessary because research suggests that it doesn't have much effect in most cases.

How amniocentesis is performed

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 foetus. 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. 

Is amniocentesis painful?

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.

How long does it take?

The procedure usually takes around 10 minutes to perform.

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.

Recovering after amniocentesis

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:

• persistent or severe pain
• a high temperature of 38C (100.4F) or more
• chills or shivering
• discharge or clear fluid coming from the vagina
• contractions (when your abdomen tightens then relaxes)

Getting the results

The first results should be available within a few days, and this will tell you whether a major chromosome problem has been discovered.

If rarer conditions are also being tested for, it can take two to three weeks or more for the results to come back.

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.

Read more about the results of amniocentesis.

After amniocentesis has been carried out, the sample of amniotic fluid will be sent to a laboratory for testing.

Getting the results

The first results should be available within three working days, and this will tell you whether a major chromosome problem such as Down's syndrome has been found.

If rarer conditions are also being tested for, it can take two to three weeks or more for the results to come back.

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.

How reliable are the results?

Amniocentesis is estimated to give a definitive result in around 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.

What the results mean

For many women who have amniocentesis, the results of the procedure will be "normal". This means that none of the genetic disorders 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 possible genetic disorder.

If your test is "positive", your baby has one of the disorders it was tested for. In this instance, the implications will be fully discussed with you and you'll need to decide how to proceed.

What happens if a problem is found

If the test finds that your baby will be born with a genetic disorder, you'll speak to a number of specialists about what this means.

This may be your midwife, a doctor with experience in childhood genetic conditions, a geneticist and/or a genetic counsellor.

They'll be able to give you detailed information about the condition – including the problems 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.

There's no cure for most genetic conditions, so you'll need to consider your options carefully. Your main options are:

• continue with your pregnancy while gathering information about the condition, so you're prepared for caring for your baby
• have a termination (abortion)

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 charity Antenatal Results and Choices (ARC) can also offer support and impartial 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.

Miscarriage

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 about 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 72 hours of the procedure. However, in some cases a miscarriage can occur later than this (up to two weeks afterwards).

Inconclusive results

After having amniocentesis, it can be reassuring if the results indicate that your developing baby has normal chromosomes and that there are no signs of any developmental problems.

However, you should be aware that amniocentesis can't test for every condition or disease, and it can't guarantee your baby will be born completely healthy.

Read more about the results of amniocentesis. 

Injury from the needle

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 now commonly used to guide the needle, significantly reducing the risk of injury.

Infection

As with all types of surgical procedures, there's a risk of infection during or after amniocentesis. Infection can occur if there are bacteria on your skin or on the instruments being used.

However, severe infection occurs in less than 1 in every 1,000 procedures.

Rhesus disease

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, if necessary.

Club foot

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 deformity of the ankle and foot that's present at birth (congenital).

Because of the increased risk of a baby developing club foot, amniocentesis isn't recommended before 15 weeks of pregnancy.