The term congenital implies the presence of a defect at time of birth, therefore congenital hearing loss is where a hearing loss is present at time of birth. It is estimated that between a quarter and half of all severe to profound hearing losses are due to hereditary/genetic causes and many fall into the congenital category.
Anyone who has congenital hearing loss will have gained this through two different ways. These are "hereditary" or "non-hereditary" causes but it can sometimes be very difficult to determine which one is the factor. It can be almost impossible to determine whether a child's hearing loss is due to the combining of two recessive genes from its parents or an untoward event during pre-natal development/birthing process. It is believed that genetic issues are responsible for more than half of all of the instances with respect to congenital hearing loss.