Amniocentesis is a diagnostic test carried out during pregnancy.

It can assess whether the unborn baby (foetus) could develop, or has developed, an abnormality or serious health condition.

Things that increase the risk of an abnormality include:

• the mother's age
• the mother's medical history
• a family history of inherited genetic conditions

Why and when amniocentesis is used

Amniocentesis can be used to detect a number of conditions, such as:

• Down's syndrome – a genetic condition that affects a person's physical appearance and mental development
• spina bifida – a series of birth defects that affect the development of the spine and nervous system
• sickle cell anaemia – a genetic disorder that causes a person's red blood cells to develop abnormally

Read more about why amniocentesis is used.

Amniocentesis is usually carried out during weeks 15-20 of the pregnancy.

The procedure can be performed earlier than 15 weeks, but this is avoided if possible because it may increase the risk of causing complications or a miscarriage (loss of the pregnancy).

Read more about when amniocentesis is used.

What happens during amniocentesis

Before you have amniocentesis, a healthcare professional will explain the procedure to you, including why they think it's necessary and the benefits and risks.

They'll also tell you about any alternative tests that may be appropriate, such as chorionic villus sampling (CVS).

If you decide to have amniocentesis, you'll usually be asked to sign a consent form.

During the procedure, a needle will be used to extract a sample of amniotic fluid, the fluid that surrounds the foetus in the womb (uterus).

Amniotic fluid contains cells shed from the foetus that can be examined and tested for a number of conditions.

Read more about how amniocentesis is performed.

Possible complications

Diagnostic tests, such as amniocentesis, are usually only offered to women when there's a significant risk their baby will develop a serious condition or abnormality.

This is because the procedure is invasive (involves going into the body) and has a small associated risk of miscarriage, estimated to be about 1 in 100.

A bacterial infection is another, but rare, possible complication of amniocentesis. The risk of developing a serious infection from amniocentesis is estimated to be less than 1 in 1,000.

The symptoms of an infection include:

• a high temperature (fever) of 38ºC (100.4ºF) or above
• tenderness of your abdomen (tummy)
• contractions (when your abdomen tightens then relaxes)

Seek immediate medical attention if you've recently had amniocentesis and you experience any of these symptoms.

Read more about the possible complications of amniocentesis.

Your results

After you've had amniocentesis, the amniotic fluid sample taken during the procedure will be tested in a laboratory.

Most women's test results will be negative and their baby won't have any of the disorders that were tested for.

A positive test result means your baby has a disorder that was tested for. The implications of this will be fully discussed with you.

Read more about the results of amniocentesis.