Every human being carries some defective genes and there is no way of making sure that his or her parther is not accidentally heterozygous for the same allele. Therefore, the genetic counselor must make every effort to banish all false guilt or responsibility considerations from the discussion It must be made absolutely clear that the purpose is simply to prevent the misery imposed on the individual as well as his family through the birth of defective children.

In this paper, to prevent the birth defect and mental redadation, the methods of antenatal diagnosis by techniques for antenal diagnosis and recurrence risk figures(probability), and mode of genetic inheritance are described.

Keywords :Birth defect, Genetic counselling, Prevention, Antenatal diagnosis