Sensorineural Hearing Loss Linked to In-Utero Second-Hand Smoke Exposure

Also surprising was the finding that the biggest difference seemed to be in unilateral hearing loss. “Cigarette smoking is systemic exposure, so you would expect both ears to be affected,” Dr. Shelton told ENTtoday.

“This study provides important information for two reasons,” said Nina Shapiro, MD, director of pediatric ear, nose, and throat at the Mattel Children’s Hospital at the University of California, Los Angeles. “First, we see a hit to the auditory system in utero that manifests itself 12 to 15 years later. That’s something we usually don’t study; generally, we look at the results of maternal habits on infants and newborns. Second, they controlled for secondhand smoke exposure, which is a known risk factor for hearing loss, and they still found more hearing loss among the adolescents who had been exposed in utero.”

It is possible that hearing losses associated with SHS exposure in utero may begin well before adolescence, said Dr. Shelton. “If this effect occurs while the inner ear is forming, then you would expect it to be apparent earlier, and early hearing loss has an impact on a number of things such as speech and language development, which is why this is such an important question.”

Indeed, “it’s very likely that it’s a continuum, meaning that if we were able to check these infants annually or biannually, we might find a progression in their hearing loss,” Dr. Shapiro said. And, “if the group in this study were followed for the next 10 to 20 years, we might see their hearing loss progress even further.”

These findings also suggest that early SHS exposure, be it in utero or during childhood, may be among many environmental factors that, when added together, take a toll on hearing. Unfortunately, said Dr. Lalwani, currently “there’s no good way to tell if there is ongoing deterioration of hearing. These kids may be more susceptible to ear injuries, but right now that’s all conjecture.”

Still, the question resonates. “We sometimes see patients who are more susceptible to noise-induced hearing loss than you would expect; the hearing loss is out of proportion to their noise exposure,” Dr. Shelton explained. “Maybe there’s an environmental factor, such as cigarette smoke, that makes them more vulnerable to this type of noise damage. That’s why I think studying this issue further may be helpful.”

Implications for Otolaryngologists

Otolaryngologists can probably be most helpful in the public message arena, Dr. Shapiro said. “People think about the obvious things associated with smoking, such as pre-term delivery, asthma and all of the respiratory problems, but they don’t really think about hearing as a potential issue. If you have patients who are pregnant, or if you are an otolaryngologist who sees children of women who smoke, I think there needs to be more education on understanding the impact of hearing on child development, language, speech, interaction, school performance, how even changes as subtle as the ones seen in this study may lead to learning issues and memory issues, developmental issues. People who smoke may think their child has normal hearing because she is 3 years old and has passed her hearing test, but she may have already sustained some permanent damage.”