A new US study suggests, for the first time, that checking the hearing of newborns using a simple non-invasive test may offer the chance to find infants at risk of Sudden Infant Death Syndrome (SIDS).

The study is available as an early online edition in the journal Early Human Development.

Dr. Daniel D Rubens of the Children’s Hospital and Regional Medical Center in Seattle, Washington, US and colleagues looked at data on babies that had died of SIDS in Rhode Island, where quite detailed medical records are kept of hearing tests on newborns. They found that 31 babies that had died of SIDS had one distinctive difference in their hearing test results compared to babies that did not.

Rubens said that:

“This discovery opens a whole new line of inquiry into SIDS research.”

“For the first time, it’s now possible that with a simple, standard hearing test babies could be identified as at risk for SIDS, allowing preventative measures to be implemented in advance of a tragic event,” he added.

Rubens and colleagues carried out a case-controlled design where 31 babies that had died of SIDS were retrospectively compared to 31 babies that survived their first 12 months of life. The babies that died were individually matched to the survivors according to sex, preterm/term status, and whether they were in neonatal intensive care or a well baby ward.

The babies that had died of SIDS showed significantly different results in a test known as the “transient evoked otoacoustic emission (TEOAE) hearing screening test” compared to the babies that survived.

The TEOAE procedure is a simple, routine and affordable hearing test, administered shortly after birth that checks the signal to noise ratio of the inner ear across three different sound frequencies: 2000, 3000, and 4000 Hz. The signal to noise ratio is a way of telling if a particular sound is distinguishable in the environment of the inner ear, or if it is drowned out by random noise.

The SIDS babies had a consistent “four point lower score” on their TEOAE test of their right ear compared to their survivor counterparts. Usually, healthy babies have a stronger test result in their right ear than their left, but in this study, the SIDS babies also had a consistently lower result in their right ear compared to their left.

Rubens and colleagues concluded that:

“Newborns at risk for SIDS are currently indistinguishable from other newborns and are only identified following a later fatal event. A unilateral difference in cochlear function is a unique finding that may offer the opportunity to identify infants at risk of SIDS during the early postnatal period with a simple non invasive hearing screen test.”

Scientists already know that the inner ear has tiny hairs for conducting sound waves further into the ear and brain for processing; they also do other things like helping to maintain balance and monitor movement.

Rubens and colleagues suggest that these “vestibular hair cells” do another important job: they tell the brain how much carbon dioxide is in the blood, and any damage to them could disrupt control of respiration and put infants at higher risk for SIDS.

Rubens said further reasearch was now needed:

“We must now fully explore all aspects of inner ear function and SIDS, and analyze testing frequencies higher than those currently tested by newborn hearing screen centers.”

Referring to the work of his predecessor, Dr Bruce Beckwith, who was one of the first scientists to identify SIDS as a distinct cause of infant death in his pioneering work at the Seattle Children’s Hospital and Regional Medical Center in the 1970s, Rubens said that he felt priveleged to be following in Dr Beckwith’s footsteps, and that:

“Each new breakthrough brings us closer to making SIDS a condition of the past.”

SIDS, Sudden Infant Death Syndrome, which has also been called “crib death” (US), or “cot death” (UK), usually affects infants between the age of two and four months, and strikes boys more than girls. According to the study authors, this elusive syndrome has puzzled scientists and parents alike for centuries, and affects 1 in 1,000 newborn babies worldwide.

SIDS is the most prevalent cause of death among this age group, claiming the lives of 3,600 babies in the US every year between 1992 and 1999, according to a study published in April 2004 in the Archives of Pediatric and Adolescent Medicine.

“Newborn oto-acoustic emission hearing screening tests: Preliminary evidence for a marker of susceptibility to SIDS.
Daniel D. Rubens, Betty R. Vohr, Richard Tucker, Courtney A. O’Neil and Winnie Chung.
Early Human Development, In Press, Corrected Proof, Available online 5 July 2007.
doi: 10.1016/j.earlhumdev.2007.06.001

Click here for Abstract (DOI link).

Written by: Catharine Paddock