This is a test to check for abnormal chromosomes in your baby. Chromosomes are tiny structures that lie within each cell of the body. There are 46 chromosomes in a human cell. There are 23 from the mother and 23 from the father, arranged as 23 pairs. They determine whether you will be male or female, how you will look and, more importantly, how your body works. Abnormal chromosomes may cause conditions, such as Down s syndrome. During the test we take a small sample of the amniotic fluid, which surrounds the developing baby in your uterus. The sample is sent to the laboratory for examination.