Aneuploidies are major causes of perinatal death and childhood handicap. Maternal serum screening test is an effective screening method for detection of major aneuploidies like Trisomy 21 & Trisomy 18/13 in the first trimester of pregnancy. Detection rate for Down syndrome is 60% with a false positive rate of 5% if only biochemical risk is estimated. A combination of Nuchal translucency and biochemical tests (Combined test) has detection rate of Down syndrome 82 to 87% at 5% false positive rate. Addition of absent nasal bone status can improve detection rate up to 93% at false positive rate of 2.5%.