Overview

Amniocentesis is a test you may be offered during pregnancy to check if your baby has a health condition or chromosomal condition.

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 chance that your baby could have a health condition or chromosomal condition.

This could be because:

  • an earlier antenatal screening test has suggested there may be a health condition or chromosomal condition
  • you've had a previous pregnancy with health condition or chromosomal condition
  • you have a family history of a health condition, such as cystic fibrosis or muscular dystrophy, and a health condition 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 your baby has a health condition or chromosomal condition.

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 health condition or chromosomal condition, the implications will be fully discussed with you.

You may choose to continue with your pregnancy, while gathering information about the condition so you're fully prepared, or you may consider ending your pregnancy (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.

Around 1 in every 200 (0.5%) women who have a diagnostic test will miscarry as a result of the test.

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.

Around 1 in every 200 (0.5%) women who have a diagnostic test will miscarry as a result of the test. The risk may be higher in twin pregnancies.

If you're offered tests to look for a health 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.

Why it's offered

Amniocentesis is offered to pregnant women at risk of having a baby with a health condition or chromosomal condition. It will diagnose any health condition or chromosomal condition 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 health condition or chromosomal condition.

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

What can amniocentesis detect?

Amniocentesis can be used to diagnose a number of health conditions and chromosomal conditions including:

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 health conditions or chromosomal conditions that were tested for.

A result showing that a health condition or chromosomal 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

Around 1 in every 200 (0.5%) women who have a diagnostic test will miscarry as a result of the test. The risk may be higher in twin pregnancies.

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.

What happens

Amniocentesis involves taking a small sample of amniotic fluid so the cells it contains can be tested. Amniotic fluid surrounds the fetus (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 fetus
  • 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 fetus. 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 your results

The first results should be available within a few days, and this will tell you whether a health condition or chromosome condition 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 health condition or chromosomal condition, the implications will be fully discussed with you.

You may choose to continue with your pregnancy, while gathering information about the condition so you're fully prepared, or you may consider ending your pregnancy (abortion).

Read more about the results of amniocentesis.

Results

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

Getting the results

If your baby has a health condition or chromosomal condition, your midwife or health professional will talk to you about your result and give you time to understand what it means.

Some parents may decide to continue with the pregnancy, while others will feel that ending the pregnancy is right for them. Only you can decide what is best for you and your family.

Your midwife will help you get the information you need and will support your decision.

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.

Risks

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.

Around 1 in every 200 (0.5%) women who have a diagnostic test will miscarry as a result of the test. The risk may be higher in twin pregnancies.

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

You should be aware that amniocentesis can't test for every condition.

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.