During amniocentesis, a small sample of amniotic fluid is taken for testing in a laboratory. Amniotic fluid is the fluid that surrounds the foetus (unborn baby) in the womb (uterus). The fluid contains cells that have been shed by the foetus, which are analysed to get information about the health of your baby.
Before having amniocentesis, a healthcare professional will explain the procedure to you, and the benefits and risks. They will also inform you about any alternative tests that may be appropriate. If you decide to have amniocentesis, you are usually asked to sign a consent form.
Ultrasound scan
An ultrasound scan will be carried out before you have amniocentesis, and will be continued throughout the procedure. An ultrasound scan uses high-frequency sound waves to produce an image of your womb that is relayed to a television monitor. See the Health A-Z topic on Ultrasound scans for more information about this procedure.
The ultrasound scan will allow healthcare professionals to:
- check the position of the foetus
- find the best place to remove some amniotic fluid
- ensure that the needle can pass safely through the walls of your abdomen (tummy) and womb
Painkiller
Before the needle is inserted into your abdomen, the area may be numbed with anaesthetic (painkilling medication). This involves having a small injection into your tummy that may sting slightly. However, anaesthetic is not usually necessary because research suggests that it does not have much effect in most cases.
The procedure
Firstly, your abdomen will be cleaned with an antiseptic solution (a substance that kills germs) to prevent infection. A long, thin needle will be inserted through your abdominal wall. This 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 removes a small sample of the amniotic fluid, which will be sent for analysis in a laboratory.
For about 8 women in every 100 who have amniocentesis, not enough fluid is removed the first time the needle is inserted. If this happens, the needle is 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 is not usually painful, although you may feel slightly uncomfortable during the procedure. Some women describe feeling a pain that is similar to period pain, or feeling pressure when the needle is taken out.
Recovery
After having amniocentesis, you are usually advised to rest for 24 hours. You may have cramps (similar to menstrual cramps) for a few hours and ‘spotting’, i.e. drops of blood from your cervix (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 is not urine)
- have contractions (when your abdomen tightens then relaxes)
