One of the paraclinical testing methods that helps screen for fetal malformations at an early stage is the double test (quantifying PAPP-A and quantifying free β-hCG).

Down syndrome is one of the syndromes that causes morphological abnormalities in the fetus, making the child after birth become dull and almost lose the ability to learn. Therefore, early screening for Down syndrome in the fetus is extremely important.

PAPP-A is a placental-derived glycoprotein macromolecule produced by the trophoblast at high concentrations throughout pregnancy. PAPP-A concentrations in maternal serum increase with gestational age.

In a normal pregnancy, PAPP-A levels gradually increase. If in the first trimester of pregnancy PAPP-A levels in the mother's blood decrease, the fetus is at risk of Down, Edward and Patau syndromes.