What is a 'triple test' for Down's Syndrome?

A triple test (also known as Bart''s test or biochemistry screening) measures the level of three substances (human chorionic gonadotrophin, oestriol and alfa-fetoprotein) in your blood at around 14-16 weeks of pregnancy. It is a screening test, not a diagnostic test. This means that the result isn't a ''yes' or a 'no', but an indication of risk of the baby being affected by Down's. Therefore if your risk is 1 in 1000 of having a Down's baby as a result of this test, this is the equivalent risk of a 20 year old woman giving birth to a Down''s baby and normally no further testing is normally advised. The 'cut off' for offering invasive prenatal diagnosis is usually if your risk of having a Down''s baby is greater than 1 in 250 at term; if your risk level is higher than this then you will often be offered chorion villus sampling (CVS) or amniocentesis. These invasive tests are diagnostic, that means they will tell you for definite if the baby has Down's or not, rather than just giving a risk. They do, however, carry a miscarriage rate of about 1%.
How likely is it that my baby will have Down''s syndrome?

The risk of having a baby with Down''s syndrome is related to your age, although parents of any age can have a Down''s child. It is not related to how many children you have had, whether you have a new partner, or to drugs that you might have taken at or around the time of conception.

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