Objectives: The use of prenatal cf-DNA testing as a highly accurate screening method for aneuploidies is bringing radical changes in the field of fetal medicine. It results in decline of numbers of invasive procedures in women with high risk, based on maternal age and/or NT screening due to substitution of cf-DNA testing instead. The average age of women deciding to have cf-DNA testing is decreasing in the period of last 6 years and numbers of tests are increasing in low risk population as well. 
Methods: We present the characteristics of pregnant woman with unselected pregnancies, who opted for prenatal cf-DNA tests, performed in one private outpatient clinic in the period from 1.1. 2013 until 31.12.2018. In our study, 11137 pregnant women were screened by NT or NT and biochemistry test as first step. 639 pregnant women were included in cf-DNA additional testing. All samples were analyzed in clinical laboratory – the ISO/IEC 17025-certified clinical laboratory of BGI-Shenzhen, China. 
Results: In last six years, of total 639 pregnant women with cf-DNA testing 48.04 % were of advanced maternal age (37 years or more). 18.78 % were at high risk for T21, based on prior screening test results, 38.14 % had low risk for chromosomal abnormalities regarding age and prior screening test results. The average age of women with cf-DNA testing was similar in the last 5 years (2013: 36.1 years, 2014: 36.2 years, 2015: 36.4 years, 2016: 36.3 years, 2017: 36.2), but declined in last year (2018: 34.9 years). The proportion of women with cf-DNA testing after NT screening increased over the last 6 years (2013: 1.4 %, 2016: 9.13 % and 2018: 18.11 %). The numbers of all invasive procedures in Slovenia decreased from 5.71 % to 4.74 % from 2013 to 2017. The prominent fall we find in the age 37 years or more: from 37.24 % in 2013 to 24.12 % in 2017 and in women aged 35-37 years: from 9.66 % in 2013 to 6.07 % in 2017. 	
In general, cf-DNA testing had 100 % (95 % CI: 66.4 %-100 %) sensitivity and 99.82 % (95 % CI: 98.97 %-100 %) specificity, PPV turned out to be 90 % (95% CI: 55.5 %-99.75 %) for all aneuploidies. Regarding only T21, sensitivity and specificity were 100 %. 
Conclusions: Our results confirm that prenatal cf-DNA testing represents highly accurate approach for advanced screening of most common aneuploidies. The numbers of tests in high and low risk pregnant women are increasing. The average age of women using cf-DNA screening, declines. The numbers of invasive procedures declines as well, particularly in the group of women aged 35 years or more.

PRENATAL CF-DNA SCREENING FOR DOWN SYNDROME AND OTHER CHROMOSOMAL ABNORMALITIES IN UNSELECTED PREGNANCIES IN SLOVENIA