A laboratory technique called fluorescence in situ hybridization (FISH) screens for numerical abnormalities of specific chromosomes. If the number is abnormal, this is called aneuploidy. In couples with known chromosome translocations, FISH may also be used to look for unbalanced translocations in the embryos. Aneuploidies and unbalanced translocations may result in pregnancy loss or the birth of a child with birth defects