Need info for down syndrome baby

Doctors say im having ds baby the blood test at 18weeks came back with me having 26% chance for ds baby im 25 yrs old this is my 3rd child and its the first time im experiencing these things at 21wks they said he had heart defect but when they looked again it was normal then at 25wks it went to a problem with his liver but they looked again and their was nothing wrong...i didnt want to to get the amnio. Cause of the risks but they have been telling he is for sure ds baby so i dnt think i need to get fluid test done when they already said he was now im 29 wks he is 1lb 14oz. Underweight. He measures small so they keep saying he may not survive which is hard to hear cause I never experienced anything like this so info that can help me would b great its hard to hear hes not going live but they don't kno for sure its all up to God..