Prenatal screening tests of genetic disorders are routinely performed in mode day obstetrics to diagnose fetal genomic abnormalities including trisomies 13,18 and 21.These include amniocentesis and chorionic villi sampling,both of which are invasive testing processes and post a small but significant risk to the fetus (Evans and Wapner 2005).Other non-invasive methods such as pelvic ultrasound as well as mateal serum biomarkers measured at various phases of pregnancy are available to detect Trisomy 21 and some other congenital disorders (Malone et al.,2005).However,these tests are often designed for disease-specific diagnosis and not helpful in identifying defects at the whole genome level.