Difference between harmony (nipt) and maternal serum screening?

Hi everyone!

I have my first OB appointment tomorrow and I know he is probably going to ask me if I'm wanting to pay for the harmony test. I know the test is going to cost money, so just want to see if it's worth it and what the difference is between the two tests, I can't seem to find an answer online aside from the nipt being more accurate possibly and providing gender.

Thanks!