The incidence of numerical chromosome aberrations is about 5% during the entire 
pregnancy and about 0.2% in live-born infants. Most commonly observed numerical 
aberrations in live births are trisomies of chromosomes 13, 18, 21, X and Y and 
monosomy of the X chromosome. It is estimated that approximately 70-80% of 
newborns with aneuploidies are born by women who did not present obvious risk 
factors, therefore, according to a recent recommendation by PTG, prenatal 
diagnosis increasing the detection of fetal aneuploidy should be offered to the 
entire population of women. Due to the risk of complications associated with 
invasive tests and a large number of unnecessarily performed tests of this type, 
it is postulated that invasive diagnostics should be used in very specific 
cases, and a non-invasive diagnostics should have a screening character 
Non-invasive diagnostics include: 1) detailed ultrasonography performed in 11-13 
(+6 days) hbd and in 18-24 hbd; 2) biochemical tests: PAPP-A (first-trimester 
test) and the triple test (second-trimester test) and less frequently performed: 
double, quadruple, and integrated tests. High detection rate of chromosomal 
aberrations in non-invasive tests (at least 75%, with no more than 5% risk of 
obtaining false positive results) and lack of procedure-related pregnancy losses 
constitute the advantage of noninvasive prenatal diagnosis.