To use the results of second trimester Down’s syndrome screening, analysis the relevance of serum AFP, uE3 and a median multiple of β-HCG with gestational age and weight , in order to improve the rate of detection and accuracy for Down syndrome screening. According to the median of 5823 cases of alpha-fetoprotein (AFP) of 15-21 weeks pregnant, human chorionic gonadotropin (β-HCG) and unconjugated estriol (uE3) to calculate AFP, uE3, value of MoM for β-HCG and assess the risk, analysis relevance of gestational age, weight and markers of three serum. Age, weight and markers of three serum are correlated. The markers of normal fetal maternal serum is AFP, levels of uE3 were positively correlated with gestational age; levels of β-HCG were negatively correlated with gestational age; maternal serum AFP, uE3, levels of β-HCG were negatively correlated with maternal weight. AFP, β-HCG, uE3 triple screening of high-risk fetuses in favor of early diagnosis and early intervention to reduce the rate of birth defects in newborns.