In prenatal diagnostics, interphase FISH (iFISH) can be used to detect certain numerical chromosome aneuploidies. iFISH in native amniocytes can be performed from the 12th week of pregnancy until the third trimester. Alternatively, the aneuploidy screening set described here is also suitable for short-term or native chorionic villus samples (CVS) without metaphases as a rapid screening test for the most common aneuploidies. This test also helps to distinguish between culture-induced or true fetal triploidy or tetraploidy (mosaicism), which occasionally occurs in parallel cell culture; in this setting, native cells are evaluated that reflect the actual fetal status. Commercially available chromosome-specific DNA probes for chromosomes 13, 18, 21, X, and Y are routinely used for this purpose. This allows trisomies of chromosomes 13, 18, and 21, gonosomal aberrations, and tri- or tetraploidy to be identified. False-positive results are possible but rare.