Introduction: Prenatal diagnosis of trisomy 21, 18 and 13 plays a very important role in the improving population quality. This study was aimed at (1) Identifying the prevalence of trisomy 21, 18 and 13 by QFPCR from amniotic cells of high-risk pregnancies; and (2) Evaluating the association between diagnosed trisomies and some characteristics of mother and fetus. Objectives and methods: 170 pregnant women with high risk of having trisomy 21, 18 or 13 fetuses during first trimester screening (gestation age from 11 weeks to 13 weeks 6 days). DNA was extracted from amniocytes for prenatal diagnosis using QF-PCR. Results: The prevalence of trisomies was 9.4%, among which trisomy 21 and trisomy 18 accounted for 68.8% and 31.2%, respectively; none of them was trisomy 13. There was the significant association between diagnosed trisomies and maternal age (cut-off 30.5 years old) and nuchal translucency thickness (cut-off 1.95 mm). MoM median of free β-hCG increased in trisomy 21 group (4.35, p = 0.021) and decreased in trisomy 18 group (0.13, p < 0.001) as compared to the non-trisomy group (2.28). MoM median of serum PAPP-A decreased in trisomy 18 group (0.14, p = 0.004) as compared to the non-trisomy group (0.54). Conclusion: Prenatal diagnosis by QF-PCR detected remarkable prevalence of fetuses with trisomy 21 và 18. There was the significant association between diagnosed trisomies and maternal age, nuchal translucency thickness, free β-hCG and serum PAPP-A. Key words: prenatal diagnosis, trisomy, QF-PCR