What is more accurate?

Is the 20 weeks anatomy scan more accurate for telling gender, or is a blood test more accurate? We got our genetic testing done today and they are going to tell us the gender in 2 weeks when they get the results of everything back (I guess they do gender when they do the genetic testing, atleast where I'm at they do) so we will know soon if we have a boy or a girl but we are also going to confirm it with the anatomy scan just to be positive. But I was just wondering if one is more accurate than the other? Or are they pretty much the same?