MONDAY, March 21 (HealthDay News) -- Newborn hearing screenings don't detect all children at risk for hearing loss, a new study finds.

Researchers in Illinois examined data from 391 children who received cochlear implants in the state from 1991 to 2008, and found that nearly one-third of children who received the implants had passed newborn screening tests but were later diagnosed with hearing loss.

Cochlear implants are small electronic devices that are surgically implanted and stimulate the auditory nerve to enable the deaf or severely hard-of-hearing to process sound.

The study included 264 children born before universal newborn hearing screening (UNHS) became mandatory in Illinois in 2003 and 127 children born after screening became mandatory.

Children born after the UNHS law took effect were younger when they were diagnosed with hearing loss than children born before the mandate, according to the study.

Children born post-mandate were also younger when they were diagnosed with severe to profound hearing loss, and younger when they received cochlear implants compared to those born before the mandate.

Spotting deafness or hearing loss early is important in helping kids develop speech and language skills, experts have found.

"Almost one-third of our pediatric implant recipients pass UNHS and are older at the time of initial diagnosis and implantation than their peers who fail UNHS," Dr. Nancy Melinda Young, of Children's Memorial Hospital in Chicago, and colleagues reported.

Some of the children who passed the newborn screening test may have had "delayed onset" hearing loss, which "limits our ability to achieve early diagnosis and implantation of a significant number of deaf children," the authors concluded.

The study is published in the March issue of the journal Archives of Otolaryngology -- Head & Neck Surgery.

More information

The U.S. National Institute on Deafness and Other Communication Disorders has more about newborn hearing screening.