well...i think there is a twist to it that makes it slightly more complicated them that....the lab tech actually got on the phone and explained it to me...which was really cool.... she said that some pregnancys.....very early on start out with two embys and one may absorb or dissolve... which is kinda common....so she said if someone didn't have an early ultrasound to know if this has or hasn't occured then it could through the test off if the blood is taken too early. After ten weeks they know how much of the fetal dna should be present per fetus. That is why you have to do it 10 weeks or later. At that point it's pretty much foolproof! YAY!! I could still do flips!