Abstract: Down’s Syndrome, which also named Trisomy 21，is the first discovered and the most common autosomal disease in human being. It is with serious harm and high incidence of abiogenesis. It has an important significancefor prenatal screening. Pregnancy assoociated plasmaprotein A(PAPP-A) is an effective maternal serum markers of Down’s syndrome screening at the early pregnancy, and the effect of the single detection is equal to or better than the other serum markers. The best combination of the double-detection is PAPP-A+β-hCG. The multiple-detection with NT improved obviously, and PAPP-A is the most promising index of Down’s syndrome screening at the early pregnancy. At present, the main screening index is only for the single-pregnancy, and the screening index of twin pregnancy is lack of a unified, common value standards which need to be improved.

Key words: Twin pregnancy, Down’s syndrome, PAPP-A, Screening, Early pregnancy