An amniocentesis is a test which is done during pregnancy to test whether your baby has any chromasomal disorders. This can be done as early as 11 weeks of gestation but usually isn’t done until after 15 weeks when the risk of miscarriage has dramatically reduced.

The most common birth abnormalities which are screened for are those which cause the baby to be born with an extra chromosone such as Down’s Syndrome, Edward’s Syndrome and Patau’s Syndrome.

Amniocentesis is offered if a woman’s age, family history or medical history put her at a higher risk of her baby having an abnormality. As it can increase the risk of miscarriage it is not offered unless a doctor thinks it it necessary. Despite this it is not a mandatory test and after discussing your options with your doctor you can choose not to have the test. Whether to have the test or not can be a simple decision for some people but a very difficult decision for others.

It can also test the maturity of your baby’s lungs. This is usually done if your doctor is considering inducing you early or doing a C-section in advance of your due date. It gives the doctor an idea of how well your baby will be able to breathe on it’s own. If you go into pre-term labour which is still in an early enough stage to stop then a doctor may use the fetal lung maturity to decide whether to stop the labour or let it continue.

Amniocentesis tests are also called chorionic villus sampling or CVS. They are done by inserting a needle into the placenta through the stomach and extracting amniotic fluid for testing. An ultrasound is used to help the doctor to guide the needle.