Invasive diagnostic tests (CVS and amniocentesis) can tell you for certain if your baby has a chromosomal condition. Screening tests cannot do this. They are called invasive procedures because they involve passing a very fine needle into the body. This means CVS and amniocentesis carry a small risk of miscarriage.
The risk of miscarriage can make both deciding to have the test and actually having the procedure very worrying.
Invasive diagnostic testing and twin pregnancies
Performing CVS or amniocentesis in twin pregnancies is more technically difficult and so the risk of miscarriage is higher. We strongly recommend that if you are carrying twins and planning to have an invasive test that you have it done at a specialist fetal medicine unit where the doctors will be experienced in dealing with twin pregnancies.