Numerical aberrations of autosomes 13, 18, 21, and sex chromosomes X and Y account for 95% of birth defects in newborns. FISH applied to uncultured amniocytes provides a method to identify those aberrations much faster than conventional chromosome analysis. It has become a standard to provide preliminary results for the detection of anomalies in less than 12 hours.
Repetitive sequences around the centromeric region of chromosome 18 can reliably determine Edward's syndrome, while chromosome X and Y specifically detect Klinefelter syndrome (47,XXY), Triple-X syndrome (47,XXX), Turner syndrome (45,X0), and 47,XYY.