There are screening test and diagnostic test available to pregnant women.
Screening test estimates the risk of the fetus having Down syndrome.
"Triple screen" is a screening test which measures the three substances in the blood (alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol). When calculate with maternal age and gestational age, it can estimate the risk of having a child with Down syndrome.
This test is offered between 15-20 weeks of gestation.
Diagnostic test tells if the fetus actually
has Down syndrome.
The diagnostic test is chromosome analysis in chorionic villi, amniotic fluid, or fetal blood.