Low PAPP-A values need to be suspected to be due to fetal chromosomal abnormalities. PAPP-A stands for serum pregnancy-associated protein A. It is one of the indicators used to screen for Down syndrome during pregnancy. The concentration of PAPP-A in pregnant women during normal pregnancy is 1.0 MOM. Early Down’s syndrome screening screens for PAPP-A around the third trimester of pregnancy.Normally, as the number of weeks of pregnancy increases, the placenta and meconium produce large amounts of pregnancy-associated proteins that are released into the mother’s bloodstream. Fetal development can be assessed by measuring pregnancy-associated proteins. In a normal pregnancy, the pregnancy-associated protein concentration is 1.0 MOM, and it decreases when the fetus has trisomy 18 or 21. If the fetus is chromosomally normal, the normal value of PAPPA is usually greater than 1 MOM. However, if the fetus is Down’s syndrome or has trisomy 18, the PAPPA value is usually less than 0.44 MOM, so it is possible to use the PAPPA value, as well as the risk of trisomy 21, to determine the specific condition of the fetus.