Objective: The aim of the study was to evaluate the effectiveness of prenatal screening for trisomy 21 with the use of the FMF angle measurement, depending on the disease risk group. Material and methods: The study included 2,026 single pregnancy fetuses, examined in years 2009-2011. The crown-rump length, nuchal translucency and frontomaxillary facial angle were measured for each of the fetuses according to the Fetal Medicine Foundation guidelines. All ultrasound exams were performed using trans-abdominal probes paired with Voluson 730 Expert and Expert E8 systems. All physicians conducting the exams were FMFcertified professionals. Maternal age at the time of the study was also reported. In 1621 pregnant women serum concentration of PAPP-A was determined using Delfia Express system (Perkin Elmer). Astraia software was used to assess fetal risk of trisomy 21. The final analysis included 791 fetuses which were followed up for the occurrence of trisomy 21. Data were analyzed using PQStat package ver. 1.4.2.324. Highly significant likelihood was set at p<0.01 and significant likelihood at p<0.05. Results: Average maternal age was 31.42 years (median: 32 in a range from 27 to 45). Average FMF angle was 76.24 degrees (median: 75 degrees in a range from 69 to 04). Average CRL measurements was 63.70 mm (median: 64.10mm in a range from 45 to 84). Avrage NT measurement was 1.91 mm (median: 1.6 mm in a range from 0.50 to 9.3). There was no significant (p> 0.05) correlation between maternal age and FMF. Highly significant (p<0.01) negative correlation between the CRL and the FMF angle was found. There were 41 fetuses with trisomy 21 (Down syndrome) in the study group. In the normal karyotype group, the FMF angle was highly significantly lower (p <0.0001) than in the trisomy 21 group. 95th percentile of the each of four separated CRL ranges was calculated. Detection rate and false positive rate for each of four different risk levels were estimated. They were used as cutoff points for two models of first trimester screening compared: Model 1, including maternal age, NT measurement and PAPP-A test, and Model 2, including maternal age, NT measurement, PAPP-A test and Frontomaxillary facial angle measurement. Conclusions: 1. Detection rate (DR) of the Down syndrome increases after the introduction of FMF angle measurement as an additional component of screening including maternal age, NT measurement and PAPP-A test. 2. Introduction of the FMF angle as an independent marker for fetal trisomy 21 risk requires further research on large populations.