Down syndrome (trisomy 21) is considered to be the most frequent etiology of mental retardation and it is the predominant reason for women seeking prenatal diagnosis. The current gold standard for diagnosis of trisomy 21 is provided by invasive sampling of fetal genetic material through chorionic villus sampling (CVS) or amniocentesis followed by conventional cytogenetic. Now in present molecular era various  molecular techniques have been developed for rapid diagnosis of Down syndrome. In review the principles, pros and cons of various techniques involved in invasive and noninvasive prenatal diagnosis of Down syndrome are discussed. 

Keywords: Down syndrome; Trisomy 21; Prenatal diagnosis.