RESUMO
Objective To approach the efficiency of second-trimester prenatal screening using two serum markers for Down's syndrome (DS).Methods Retrospective analysis was conducted on the results of prenatal screening using two serum markers,alpha fetoprotein (AFP) and free beta subunit of human chorionic gonadotropin(free-β-hCG),in 50 cases of DS pregnancy identified among 60 931 pregnant women received prenatal screening from November 1997 to April 2008 in Nanjing Maternal and Child Health Hospital.Results Among the 50 DS cases,the detection rate of DS was 50% (25/50) when taking free-β-hCG≥2.5 MoM as the cut-off,with the positive rate of screening was 6.6%.And the detection rate of DS would be 18.0%(9/25) when taking AFP≤0.5 MoM as the cut-off,with the positive rate of screening was 4.6%.When the risk cut-off value of DS was set at 1/270,the detection rate changed to 52.0%,and the positive rate of screening was 4.7%;and the two figures changed to 62.0% and 5.5%,respectively,when the risk cut-off was set to 1/300.Thirteen DS cases showed the risk value between 1/1000 and 1/300,among which two were monomarker abnormality.Thirteen (26.0%) of the 50 DS fetus were found to have one or two abnormality markers by ultrasound scan,among which one was DS low risk,and the other 12 were DS high risk in serum screening.Conclusions The second-trimester prenatal screening using AFP or free β-hCG for Down's syndrome is effective in identifying DS pregnancy with limited specificity and sensitivity.But the detection rate can be elevated by the combination of these two markers.The second trimester systemic ultrasound scan is not ideal for DS identification,but it can increase the specificity and sensitivity of serum prenatal screening.