The current maternal blood-screening test is called the triple screen because:

The current maternal blood-screening test is also known as the triple screen test because of the testing of the three substances in the blood of a pregnant woman. These three tested components are the hCG (Human Chorionic Gonadotropin), AFP (Alpha-feto protein), and the estriol.

For the purpose of this triple screen test, the blood is drawn for the expectant mother and then this drawn blood is tested for the listed three components.

Hence, the correct answer is 'it tests for three substances in the maternal blood'.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."