The diagnosis of Down syndrome can be made before the baby is born.

A blood test may be performed between 74 to 94 days into a pregnancy, in order to screen pregnant women for Down syndrome. Combined with pregnancy ultrasound, this test can detect 85% of cases of Down syndrome.

In some cases, a special test, called amniocentesis, may be needed to detect Down's syndrome. During amniocentesis, a physician uses a syringe to remove a sample of the amniotic fluid that surrounds the fetus. After culturing the fluid, fetal cells are analyzed for their genetic make-up.