Objective:To optimize and evaluate the value of fluorescence in situ hybridization(FISH)for the prenatal diagnosis and pre-implantation genetic diagnosis(PGD)of Down Syndrome.Methods:FISH with two-color fluorescence-labeled 21 and X chromosomes probes was conducted to analyze normal samples,peripheral blood samples of 25 children with Down syndrome and amniotic fluid samples of 10 pregnant women(positive for serum screening).The result of cell culture for karyotype analysis was used as the gold standard for...