Antenatal Diagnostic Tests
One of these tests are usually offered and undertaken if the screening test (see above) is 'high risk'. However, women above the age of 35 years are sometimes still offered these tests based on their age alone as an indicator or 'high risk'.
Chorionic Villous Sampling (CVS)
This test is performed at 10 to 12 weeks. Under ultrasound guidance, a fine needle is used to remove a small sample of tissue from the placenta. This tissue can provide genetic information from the baby. The advantage of CVS is it can be performed early in pregnancy, but the associated miscarriage risk is around 1-2%.
Amniocentesis
This test is performed at 15 to 17 weeks. It can also be performed at any time later in pregnancy if necessary. This is a test for genetic or inherited conditions such as Down syndrome or cystic fibrosis. Under ultrasound guidance, a fine needle is used to remove a small sample of amniotic fluid from around the baby and the baby's cells are extracted from it. Results are available in two weeks and are highly reliable, although there is an associated miscarriage risk of around 0.5-1%
