PAPP-A is the pregnancy-associated protein. Normally, as the number of weeks of gestation increases after pregnancy, the placenta and meconium tissue produce large amounts of glycoproteins, also known as pregnancy-associated proteins. These specific pregnancy-associated proteins are released into the mother’s circulation, and by measuring the pregnancy-associated proteins in the mother’s blood, the baby’s development can be assessed. When a baby has trisomy 18 or trisomy 21, the concentration of pregnancy-related proteins in the mother’s blood is significantly lower, so this test can be used to screen for Down’s syndrome and trisomy 18. However, this test is only clinically significant in early screening, but not in mid-term screening. If the screening result is abnormal, further tests are needed to clarify the diagnosis.