ABSTRACT
<p><b>OBJECTIVE</b>To screen and diagnose Down's syndrome during mid-term pregnancy to reduce the number of babies with Down's syndrome.</p><p><b>METHODS</b>With the multi-level of stratified cluster sampling, twenty thousand and eight hundred and three women at 15-20 weeks gestation were screened by maternal serum AFP and beta-hCG using the time resolved fluoroimmunoassay (TRFIA). Then the screened high-risk women were diagnosed by amniocentesis, cell culture and chromosome analyses. The born children were diagnosed by follow-up and peripheral blood chromosome analyses.</p><p><b>RESULTS</b>Six fetuses were diagnosed by serum screening and amniotic fluid chromosome analyses, and 3 born children were diagnosed by follow-up and peripheral blood chromosome analyses. Nine cases of Down's syndrome were detected in total, with the positive prenatal screen rate being 67% (6/9).</p><p><b>CONCLUSION</b>The prenatal screening and diagnosis can reduce the birth of Down's syndrome patients and improve the population quality. However, the diagnosis accuracy still needs to be improved to further reduce the false negative rate and prevent misdiagnosis.</p>