['The cause of aneuploidy in fetuses of young women is not fully understood. As such women are considered to be at risk of repeating the "error", it is customary to recommend chromosomal evaluation (karyotyping) in subsequent pregnancies. Individuals predisposed to meiotic nondisjunction exhibit aneuploidy in their mitotic cells (mosaicism). The aim of this study was to assess the actual risk for repeated aneuploidy in patients who had a previous pregnancy with aneuploidy by estimating the rate of somatic random aneuploidy in their normal pregnancy and to assess whether this risk is heritable. With utilization of FISH, we assessed the number of chromosomes 9 and 18 in amniocytes from the following pregnancies: 1. Fourteen of the women had a history of chromosomal aneuploidy in a previous pregnancy (study group). 2. Ten women had previous normal pregnancies (control). 3. Nine samples were assessed in amniocytes taken from aneuploid pregnancies (positive controls). A mean of 458+/-65.66 amniocytes were evaluated (range 97-500 nuclei). There was no significant difference in the rate of aneuploidy of both chromosomes between the study and control groups. However, this rate was significantly higher in the aneuploid pregnancies (p < 0.05).'] Does previous aneuploidic offspring in a young woman increase the risk for somatic random aneuploidy in subsequent pregnancies?