Objective:To investigate the efficiency of maternal serum triple screening for the genetic abnormality in second-trimester and the morbidity of adverse pregnancy outcome in false positive results of the test. Methods: A total of 4 680 pregnant women with singleton pregnancies assigned in Obs & Gyn Hospital, Fudan University, underwent triple screening test (alpha fetoprotein, AFP; human chorionic gonadotropin, HCG and unconjugated estriol, uE3) by fluorescence enzyme immunoassay between 2003 and 2005. The valid MoM (Multiples of Median) value of mid-trimester serum AFP, uE3, and hCG and risk assessments was provided by Beckman Coulter Co. When applied in the prenatal Down syndrome screening service. The study compares the incidence of chromosomal abnormalities with Down syndrome in screen positive women and compares to the MoM value established in the literature. The risks of having a fetus with congenital abnormalities or of developing obstetric complications in the screen positive women with their matched controls.Results:The MoM values for the triple tests of our study are similar to established values of literature. Only 51.01% women with pregnancies agree to receive screening. Amniocentesis utilization rate was 55.12% in the screen-positive pregnancies. The false positive rate was 6.89% and the median of maternal age of the women was 28.13 (range 19 to 49) years old. Chromosomal abnormalities were identified in 21 pregnancies, including 9 cases of trisomy 21.The detection rate was 77.77%. Pregnancies with positive screening results had a significantly higher risk of adverse outcomes than those with negative results (P< 0.05). Whereas there was no difference in the incidences of fetal congenital appearance or skeleton abnormality. Conclusion: Adjusting MoM values of local unaffected populations is limited to increasing the detection rate. Because chromosomal defects have variable exhibitions, amniocentesis utilization is still a choice for screen-positive pregnancies. Screen-positive pregnancies had increased risk of chromosomal abnormalities.