美国60％以上的孕妇产前作血浆测定,以筛选开放性神经管缺损及唐氏综合征,其筛选的基础是由胎盘合成分泌的特定物质进入母体循环后趋于异常。唐氏综合征妊娠胎儿生成的甲胎蛋白(AFP)与非结合雌三醇(uE_3)减少,而胎盘产生的人绒毛膜促性腺 More than 60% of pregnant women in the United States prenatal plasma test to screen for open neural tube defects and Down Syndrome, the screening is based on the placental synthesis and secretion of specific substances into the maternal circulation tends to be abnormal. Downstream fetuses produce fetal alpha-fetoprotein (AFP) and unconjugated estriol (uE_3), while placental production of human chorionic gonadotropin