Hearing tests routinely administered to most newborns may soon be used to identify children who are at risk of sudden infant death syndrome, or SIDS, according to Seattle researchers.
Records of hearing tests administered to 62 infants in Delaware show that those who later died of SIDS had a unique pattern of partial hearing loss, according to a report this week in the journal Early Human Development.
"This discovery opens a whole new line of inquiry into SIDS research," said lead author Dr. Daniel D. Rubens of Children's Hospital and Regional Medical Center in Seattle.
About 3,600 children die of SIDS each year, generally when they're 2 to 4 months old and typically in their sleep.
Although campaigns to have infants sleep on their backs have reduced the mortality rate, no cause for the deaths has been proved.
One suggestion is that the deaths are caused by disturbances in respiratory control. The vestibular apparatus of the inner ear has been shown to play an important role in respiratory control during sleep. Rubens speculated that inner ear damage could be linked to SIDS.
Using Delaware health records, which has the longest history of newborn hearing screening, he and his colleagues examined the hearing tests of 31 infants who died of SIDS and 31 controls.
In the tests, called transient otoacoustic emission, a tiny probe is inserted in the ear and emits a clicking sound. The instrument measures the electrical response emitted by hair cells in the ear.
They found that the SIDS infants had a 4-point loss of hearing sensitivity in their right ears at each of three frequencies between 1,000 and 4,000 hertz.
The fact that the loss is the same at all three frequencies means "it is not occurring by chance," Rubens said.
Infants in the control group had higher hearing sensitivity in their right ears than in their left ones -- the reverse of the SIDS infants.
Rubens speculated that the damage occurs during delivery, particularly when prolonged contractions create greater blood pressure in the placenta. The right ear, he said, is directly in the "line of fire" for blood entering the fetus from the placenta, and thus could be most susceptible to damage.
If the findings are correct, he said, it may be possible to take corrective measures.
Researchers are beginning animal studies to explore the connection.