Amniocentesis

An amniocentesis is one of a number of tests which can be carried out during pregnancy. It is commonly used as a diagnostic tool to detect any chromosomal abnormalities in the genetic makeup of an unborn baby which could cause a condition or abnormality, such as Down's syndrome and spina bifida.

What is an amniocentesis and what does it involve?

The procedure is carried out in hospital and involves the insertion of a needle through both the mother's abdomen and the lining of the womb. This is to retrieve a sample of the amniotic fluid, the liquid which surrounds the baby. A very fine needle is used and is guided into the amniotic sac by using a handheld ultrasound device. Approximately 20 millilitres of amniotic fluid is taken from the sac. This sample contains cells from the baby, which will be analysed and tested in a laboratory for markers of certain genetic disorders.

The procedure itself usually only takes five to ten minutes and should not be too uncomfortable for you. You will need to lie down and try your best not to move while the sample is extracted. The baby will be totally unaware of everything so there is no need to worry about them. You will be allowed to go home straight away but you'll need to rest for the rest of the day. You may experience some stomach cramps, but if this is accompanied by any unusual discharge or bleeding, then you must seek medical help immediately.

Why might I be offered an amniocentesis?

In some regions of the United Kingdom, mums-to-be are offered blood tests. The results of these are used, combined with the mother's age, to calculate the level of risk there is of the baby developing Down's syndrome. Down's syndrome is a genetic abnormality which affects physical appearance and mental development. If the result of this blood test shows a high risk, normally 1 in 250 or less, then you will most probably be offered an amniocentesis.

A special ultrasound scan called nuchal fold is also routinely offered to some women. During this the thickness of the skin at the back of the baby's neck is calculated. The thicker this fold of skin, the higher the chance of the baby developing Down's syndrome. Even at anomaly scans, usually carried out at 20 weeks, markers and features which could indicate a defect are checked. Again, if there is any doubt an amniocentesis can be requested.

A woman who has already experienced a pregnancy affected by a genetic disorder such as Down's syndrome, spina bifida - a birth defect which affects the spinal and nervous system - or the blood condition sickle cell anaemia, will automatically be offered an amniocentesis. Likewise, you can also request an amniocentesis if you so wish.

Do I have to have an amniocentesis?

An amniocentesis is only carried out after 16 weeks of pregnancy and is only offered to women whose babies are at high risk of having an abnormality or disorder. You are well within your rights to disagree to the procedure. It is a procedure which, unfortunately, does carry risks as it penetrates the amniotic sac. This can, in rare cases, trigger a miscarriage. The procedure will be well explained to you if you are offered the test, and you will also be given as much information as possible about why the test has been recommended. You will be able to discuss what the test might tell you as well as the risks involved if you do decide to go ahead. You are likely to be offered counselling to assist you in making the best choice for you. You will also be encouraged to think about what you would do if the results uncover a problem in an effort to ensure you reach the right decision for you. You can be assured that the amniocentesis will be carried out with the best care and attention to minimise any risks.

When will I know the results and what happens next?

Initial findings are sometimes available within 48 hours, with a full report ready after two to three weeks.

Unfortunately, there is no cure for genetic disorders and, therefore, the decision about whether to continue with the pregnancy lies with the parents. You will be supported throughout the process and will have many opportunities before, during and after an amniocentesis to discuss your thoughts and feelings on the possibility of your unborn baby being affected by a condition or abnormalities.