Prof. Attias then found another five children who had been referred to him for pre-operative testing who had begun to hear. At the end of his clinical research, he identified a "window of opportunity" of 17 months during which deaf children may begin to hear. "A child whose deafness is caused by a malfunctioning connection between hair cells and the auditory nerve should not have a cochlear implant in the first 17 months of life. Research results show the possibility that at least some of these children undergo the procedure for nothing," explained Prof. Attias.
http://www.news-medical.net/?id=25272
This is something I've been concerned about for years due to the issues with hearing tests for babies not always being accurate. Now it turn out that there's a possibility that some babies are born deaf only to start hearing within a year or two.
So, how do one truly determine if a baby is deaf or not?