Extra testing

The doctors have asked me the past couple visits and if I wanted to do all the extra testing for Down syndrome and other stuff. I told them no because we have heard and read that with two babies the test are more inconclusive or way off. No matter what we will love our children. I was just wondering yalls thoughts on the test. If the test were worth it? Did the test turn out weird? It's just a lot of money on test that they say may or may not work.