Amniocentesis - Introduction

Amniocentesis is a diagnostic test that is carried out during pregnancy. It can assess whether the unborn baby (foetus) could develop, or has developed, an abnormality or serious health condition.

Factors that could increase the risk of an abnormality include:

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

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 condition that causes unusually shaped red blood cells

The procedure

Amniocentesis is carried out after week 15 of the pregnancy. A needle is used to extract a sample of amniotic fluid, the fluid that surrounds the foetus (the developing baby) in the womb (uterus). The amniotic fluid contains cells shed from the foetus that can be examined and tested for a number of conditions.

Chorionic villus sampling (CVS) is an alternative diagnostic test that can be carried out during weeks 10 to 13 of pregnancy. See the Health A-Z topic about CVS for more information about this procedure.

Outlook

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

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

If amniocentesis is recommended, the healthcare professional who carries out the test will explain why they think the procedure is necessary, as well as the benefits and risks involved.

Diagnostic tests are voluntary, and counselling should be provided to make it easier to cope with the results.