First trimester, second trimester, and integrated screening for Down's syndrome in China.

ObjectiveTo compare the effectiveness of first trimester, second trimester, and integrated screening for Down's syndrome.SettingTwo prenatal diagnosis centres in China.MethodsA total of 11,966 pregnant women (≥18 years) were screened over 21 months. First trimester screening (11–13 weeks) comprised measurement of serum free beta-human chorionic gonadotrophin (β-hCG) and pregnancy-associated protein-A concentrations, and fetal nuchal translucency thickness. Second trimester screening (15–20 weeks) comprised measurement of β-hCG and alpha fetoprotein concentrations. Computer software was used to calculate the risk of carrying a Down's syndrome fetus.ResultsThe overall incidence of Down's syndrome was 0.2% (23/11,966). When the false-positive rate was fixed at 5%, detection rates for first trimester, second trimester, and integrated screening were 73.9%, 69.6%, and 82.6%, respectively. When the false-positive rate was fixed at 3%, detection/sensitivity rates for first trimester, second trimester, and integra...