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I had a Alpha-Fetoprotein test performed last Monday. My doctor insisted I was in my 14th week. Yesterday she called to let me know that my baby had tested positive for Downs syndrome. I know when my last cycle started and know the date that I conceived...when I do the math, I am calculating that I was only in my 13th week. I am curious if a week or less than a week could make enough of a difference to erroneously judge the fetus as underdeveloped based on the test?? Does anyone know? I am driving myself crazy.