Abstract: Objective:To explore the clinical significance of serum marker at the metaphase of pregnancy in screening fetus Down's syndrome (DS).Methods:The concentration of alpha-fetoprotein (AFP) and free β-subunit of human chorionic gonadotrophin (β-hCG) in the serum of women at the metaphase of pregnancy were tested by time-resolved fluoroimmunoassay.Multiples of the median (MOM) and the risk probability were calculated concerning the age,gestation and weight of the women by homemade DS screening software.Results:Three thousand and one hundred and seventeen women at the metaphase of pregnancy were screened;177 of them were in high risk of DS,and the high-risk rate was 5.68%,which was lower than that calculated by imported analysis software.Eighty-two of the 177 high risk cases received chromosome test by amniotic fluid puncturation and 3 cases were confirmed.Two of the remaining 95 cases which failed to take amniotic fluid test resulted in spontaneous abortion,and no DS newborns were delivered in women with negative screening results.The group over the age of 35 had a higher positive rate than that below 35.The difference was significant (P<0.01).Conclusions:The double-marker test with AFP and free β-hCG in serum of women at the metaphase of pregnancy using homemade analysis software is a feasible prenatal screening technology easily accepted by pregnant women.The MOM output by homemade software is more suitable to the Chinese,which may reduce the false positive rate of screening and diminish the waste of medical resources.