Deafness accounts for the largest number of disabilities in the country, and more than 60% of congenital deafness is caused by hereditary factors. Each year, up to 30,000 children with hearing impairment are born, and for every 100 normal hearing people, 6 are carriers of the deafness gene. Even couples with normal hearing are at risk of having a deaf child because they carry the deafness gene. Hereditary deafness is passed from parent to child through inheritance or intergenerational transmission. About 90% of deaf children have normal hearing parents, and if both parents carry the same gene for deafness, the child has a 25% chance of becoming deaf. Genetic testing for deafness can identify the genetic cause and protect residual hearing. The test can be performed at various times before pregnancy, during pregnancy, and during the newborn period for early detection, prevention, and treatment. Testing for the four deafness genes can identify the cause of 90% of hereditary deafness.