Amniocentesis involves removing a small sample of amniotic fluid from the womb so the cells it contains can be tested.

Amniotic fluid surrounds the foetus (unborn baby) in the womb (uterus). The fluid contains cells shed by the foetus that can be analysed for information about the health of your baby.

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 alternative tests that may be appropriate. If you decide to have amniocentesis, you'll usually be asked to sign a consent form.

Read about the possible complications of amniocentesis for more information about the risks.

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.

The procedure

An antiseptic solution will be used to clean your abdomen to minimise infection. A long, thin needle will be inserted through your abdominal wall. It may cause a sharp, stinging sensation.

Using the ultrasound image as a guide, the needle will be passed into the amniotic sac that surrounds the foetus. A syringe will then be 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 usually takes around 10 minutes. However, it can take slightly longer if the position or movement of the foetus makes it difficult to take a sample.

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.

Recovery

After having amniocentesis, you'll usually be advised to rest for 24 hours. You may have cramps (similar to menstrual cramps) for a few hours and "spotting" (drops of blood from your cervix, located at the neck of the womb).

You should seek urgent medical attention if you:

• feel shivery
• have a high temperature (fever) of 38ºC (100.4ºF) or above
• are bleeding from your vagina
• have persistent lower back pain or abdominal pain
• have clear watery fluid coming from your vagina (that's not urine)
• have contractions (when your abdomen tightens then relaxes)