Down’s Screening is a blood test. Down’s syndrome is an obstetrical test performed between 15 and 20+6 weeks of pregnancy to screen fetuses for trisomy 21, trisomy 18, and open neural tube defects. Down’s syndrome is detected by drawing 3-5 ml of peripheral blood from the mother to measure the concentration of alpha-fetoprotein, free human chorionic gonadotropin, and estriol, which, together with the mother’s age and the week of gestation, is used to estimate the risk of the fetus having these conditions. It is recommended that you visit your local hospital’s prenatal diagnostic center for Down’s syndrome testing during pregnancy, depending on the appropriate gestational week.