An incorrect number of chromosomes is the most common form of genetic disorder that causes the fetus to spontaneously abort. The human cells normally contain 23 pairs of chromosomes, for a total of 46 chromosomes in each cell. Error in one or more of the meiosis, mitosis, maternal age, or environment are the possible cause of the chromosome abnormalities. These abnormalities in the number chromosomes can cause problems with development, growth and function of the body's systems. These changes can occur in early fetal development, or in any cell after birth during the formation of reproductive cells (sperm and eggs).