Objective To evaluate the efficiency of second trimester screenings for Down syndrome using alpha-fetoprotein and β-human chorionic gonadotropin duplex.MethodsPregnant women of south Zhejiang were screened for Down syndrome fetuses by maternal alpha-fetoprotein and β-human chorionic gonadotropin duplex during second trimester.The high-risk women underwent prenatal diagnosis by amniocentesis,cell culture and chromosome analysis.The newborns followed up by the maternal and child tertiary health care network and suspected to have Down syndrome were diagnosed by peripheral blood chromosome analysis.Statistical analysis was performed using two-sample t test and x2 test.Risk probability of Down Syndrome was calculated by random screening software. Results From Oct.2007 to May 2009,1130 of 32 188 singleton pregnant women in second trimester received prenatal screening were discovered with high risk(≥1 ∶ 270).Prenatal diagnosis was performed in 90.79％ cases (1026/1130) of high risk women and seven fetuses were diagnosed as Down syndrome by amniotic fluid chromosome analysis,and the pregnancies were terminated.Among the other 104 cases without prenatal diagnosis one Down syndrome baby was delivered.Six of 31 058 pregnancy women with low risk delivered Down syndrome babies with the incidence of Down syndrome of 0.19‰ (6/31 058).Detection rate of second trimester screenings for Down syndrome using alpha-fetoprotein and β-human chorionic gonadotropin duplex was 57.14％(8/14).False positive rate was 3.48％ (1122/32 188).Positive predictive value was 7.08‰(8/1130).During the same period,there were 23 813 pregnant women who didn't receive screening and 15 fetuses with Down syndrome were diagnosed after birth.There was no statistical difference in the prevalence rate of Down syndrome between those pregnant women who received prenatal screening or not [0.43‰ (14/32 188) vs 0.63‰ (15/23 813),x2 =1.004,P＞0.05].The prevalence of Down syndrome was 0.52‰ (29/56 001) in this area. ConclusionsThe prenatal screening and diagnosis could reduce the birth rate of Down syndrome patients.However,detection rate,false positive rate and positive predictive value of which were lower than reports in other studies.It's possible that the reference data might be not suitable for Chinese.