[Trisomy 18 and 13 and triploidy: the best way to diagnosis]

The increase in maternal age at birth, especially in modern countries, has led to increased prevalence of trisomies and other chromosomal disorders. Recently, with the discovery of the possibility to test cell free fetal DNA (cffDNA) in maternal blood, the role of the screening methods applied to detect fetuses with trisomies and triploidy, i.e. the nuchal translucency and the first and second trimester biochemical markers and fetal anomaly scan, are questionable. Meanwhile, most studies stilL show that cffDNA have a certain percentage of false positive and false negative results and different detection rates depending on the method used to analyze the fetal DNA. Meanwhile the vast majority of trisomy 13 and 18 triploidy is detected using biochemical screening and ultrasound. Therefore, the conventional screening methods should be applied and suspected cases should be karyotyped using an invasive test until we gain more experience in the cffDNA tests.