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Triple Screen Test
Tests are now available that go beyond alpha fetoprotein testing in helping your healthcare provider determine if you might be carrying a child with Down syndrome. With the triple screen test, your alpha fetoprotein level is checked, along with the amounts of human chorionic gonadotropin (HCG: a pregnancy hormone) and unconjugated estriol (a form of estrogen produced by the placenta).

The levels of these three chemicals in your blood may indicate the presence of Down syndrome. For older mothers, the detection rate of the problem is higher than 60%, with a false-positive rate of nearly 25%.

If you have an abnormal result with a triple-screen test, an ultrasound and amniocentesis may be recommended. An elevated alpha fetoprotein level can indicate an increased risk of a neural-tube defect (such as spina bifida). HCG and estriol are normal in this case.
Remember: These blood tests are used to find possible problems. They are screening tests. A diagnostic test will usually be done to confirm the diagnosis.

this is done during pregnancy.