Try not to worry because I have heard there are false positives with that testing all the time. That is why I chose not to have the test for my first pregnancy and I won't with this one either. I wish I could be more help--I am sure your doctor is right and its false.
Hey girl try not to worry I'm 17wks as well and had my DOWN screen done a couple of weeks ago it came back negative, but my specialist advised me that there was a wider chance of a "false positive" then a complete negative. He said a number of things could cause the false positive like family history, advanced maternal age, you being a carrier of the gene. So being that you have the battle half way won with non of the major factors I wouldn't worry about it too much. At most you or your baby may just be a carrier of the gene but not have the full trait. Keep praying and I'm sure everything will work out fine!
Thanks, I guess I'll know for sure on Saturday. Wish me luck.