What is the critical risk of Tang Si Jiu? Tang screening is a prenatal screening technology, mainly used to detect fetal congenital diseases. It is also called fetal birth defect risk screening in medical nutrition. Tang screening results usually include several indicators such as Tang screening value, PAPP-A, and free β-hCG. Based on the Tang screening results, doctors can assess the \”nine-fold critical risk\”, that is, the risk of fetal disease. This article will discuss the ten Tang sieve nine layers