This invention relates to assays used to detect and confirm genomic aberrations, such as chromosomes 13, 18, 21, X and Y aneuploidy as well as 22q11.2 deletions, for prenatal diagnosis. For the detection, combined STR markers (all tetra-nucleotide repeats) are employed to cover different chromosome regions. For the confirmation step, individual chromosome specific STR markers (tetra-nucleotide repeats) are utilized. This invention particularly relates to multiplex analysis for the presence or absence of STR markers in genomic DNA isolated from peripheral blood, amniotic fluid, cultured amniocytes, chorionic villi, or fetal cells existing in maternal blood. This invention offers an efficient approach to identify chromosomal abnormalities by using STR markers.