To investigate key techniques and intervention in reducing birth defects. Down's syndrome (DS), trisomy-18 (Edwards syndrome, ES), neural tube defects (NTD), Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA), thalassemia, and glucose-6-phosphate dehydrogenase deficiency (G6PD) were chosen as target disease. From Jan. 2007 to Dec. 2009, the condition of intake folic acid were investigated in 5004 pregnant women in Panlong District and Wuhua District of Kunming City. All of the 27 660 pregnant women undergoing prenatal examination were enrolled into the study from the First People's Hospital of Yunnan Province, the Second People's Hospital of Yunnan Province, the First People's Hospital of Qujing City, the Second People's of Qujing City, Qujing Women and Children's Hospital, People's Hospital of Lincang City, Kunming Maria Women's Hospital, Maternal and Infant's Care Unit of Panlong District of Kunming City, Maternal and Infant's Hospital of Dali City. The screening was performed on serum of those pregnant women at 8 - 20(+6) gestational weeks. Prenatal cytogenetic analysis and fetal ultrasonograpy were performed on the high risk or indicated women after genetic counseling. DNA analysis was administered on those women with family or childbearing history of DMD, SMA, thalassemia, or G6PD. Outcome of pregnancy was followed up to evaluate the effect of intervention. Approximately 30.10% (1506/5004) of pregnant women were administered by oral folic acid during perinatal period. Two thousand three hundred and thirteen women with high risks of DS, ES, or NTD fetuses were observed among 27 660 undergoing maternal serum screening. Two thousand and ninety-six pregnant women including two twins pregnant women were performed cytogenetic analysis. Other 67 pregnant women at high risk of DMD, SMA, thalassemia, and G6PD accepted genetic counseling and prenatal gene analysis. Two thousand one hundred and sixty-three pregnant women (2165 fetuses) underwent prenatal examination. One hundred and two cases chromosome abnormalities, 17 cases NTD, 4 cases DMD, 1 cases α-thalassemia major were found. All of the 91 fetuses with major birth defects were terminated after genetic counseling. Another affected DS fetus in a twin pregnancy dead intrauterine at 24 gestational weeks. Thirty-two women bearing fetuses with balanced translocations or inversions continued their pregnancies. Totally 2071 normal term fetuses were born in the prenatal diagnosis group. Two fetuses with normal chromosome were lost within 1 week after amniocentesis. Four affected DS fetuses were born from their high risk mothers who refused further prenatal diagnosis service. In a random sampling follow-up cohort of 5000 mothers at low risk, none of affected child suffering target diseases was found. The DS detection rate of maternal serum screening was 84% (27/32), with the false positive rate was 6.153% (1702/27 660). Folic acid intake before conception and in the first trimester would reduce the risk of birth defects, only 1/3 reproductive women took folic acid actively. Maternal serum screening could effectively detect high risk of DS, ES and NTD. The genetic counseling is critical in women at high risk or who had family history of inherited disorders. The prenatal screening and diagnosis combined with routine obstetric care could reduce the incidence of major birth defects, which should become prenatal care strategy in our country.