The invention provides prenatal screening methods for Down's syndrome. Specifically, the methods of the invention comprise determining the amount of hyperglycosylated human chorionic gonadotropin (hCG) charge isoforms in a biological sample from a pregnant woman and comparing the amount of highly acidic and less acidic isoforms with those found in a sample taken from a pregnant woman carrying a normal fetus. The methods of the invention can be employed during any stage of pregnancy.