Don't take it - we chose not to take it because the false positives are SO high all it does is cause unnecessary stress. All of the girls who decided to get it just went through an awful time posting "OMG, MY LAST TEST SHOWED MY DS RISK DOUBLED!!" The risk would still be very small, but they couldn't get it out of their head that the risk was increasing and would jump to the worst possible conclusion. They felt like that just HAD to get an amnio done (which poses a small risk to the baby) just to find out for sure because they couldn't wait. They were all so envious of all of us girls who declined and were just enjoying our pregnancies not stressing. You have to ask yourself, would you do anything differently if you found out your baby had DS? We knew we would love our baby regardless, and it wouldn't change our decision, so why stress about a false positive?
My friend got the test and it came back positive for DS, and the nuchal fold at her 20 week U/S also showed increased risk of DS and guess what - she gave birth to a perfectly healthy baby boy, no DS. She was beside herself the last 4 months of her pregnancy for no reason at all.