When is it done:
Detection rate for Down's syndrome:
The maternal serum triple test (also known as the Down's test) is a blood test that is done to measure the levels of three hormones. The test can be an indicator of a baby’s risk of neural tube defects (spina bifida) or Down’s syndrome. Care must be taken to make sure that the dating of the pregnancy is correct. Inaccurate dating may cause these hormone levels to be incorrectly interpreted. If the test is positive, it is not a positive indicator that a baby has Down’s syndrome, but rather that the mother is at a higher risk for a Down’s baby at her age compared to the norm. An invasive test like amniocentesis is still required to establish whether the baby is affected or not.
An extension of this test is the Quadruple test which tests for four chemical markers and is slightly more accurate.
The screening tests on maternal blood can be combined with the nuchal fold test to give a more accurate prediction of Down's syndrome.