Using the same criteria employed in the earlier study, the investigators identified 400 participants who were SHS-exposed and 432 who were not exposed. Data on smoking activity and cotinine measures were missing in 132 cases, but those individuals were included in the study because there was enough information for the primary analysis, which concerned maternal smoking and hearing loss in the child.
Explore this issue:October 2013
Of the 964 adolescents in the study sample, 92.8 percent of the children of nonsmokers had normal hearing, versus 82.2 percent of those born to smokers.
Children exposed to cigarette smoke in utero were more likely to sustain SNHL at all levels of severity. Most common was mild loss, at 15 to 25 decibels (dB), seen in 5.6 percent of the unexposed children and 11.9 percent of the exposed children. Moderate hearing loss (25 to 40 dB) was seen in 0.9 percent and 4.5 percent of each group, and severe loss (>40 dB) in 0.7 percent and 1.4 percent of each group, respectively (p=0.03 on the Cochrane-Armitage trend test, suggesting the existence of a trend). On bivariate analysis, 7.1 percent of the unexposed and 17.6 percent of the exposed children demonstrated unilateral low-frequency hearing loss (p=0.049). “Adolescents with prenatal smoke exposure had 2.6-fold higher odds of unilateral low-frequency SNHL than unexposed controls,” the authors wrote. The increased risk was independent of SHS exposure after birth. Bilateral and high-
frequency hearing loss were also more common in the children whose mothers smoked during pregnancy, although those differences were not statistically significant.
“This means smoking is dangerous even before you’re born,” Dr. Lalwani told ENTtoday. “There appears to be no period in life when you can escape its effects.” He also pointed out that two-thirds of the mothers who smoked quit during the first trimester, most likely as soon as they learned they were pregnant. “Yet even though the vast majority of women stopped smoking early, we could still detect an effect in the children.”
—Anil K. Lalwani, MD
At least one expert admitted that these findings were somewhat surprising. “I thought this was a well-designed study with a large number of patients, of an important public health problem,” said Clough Shelton, MD, chief of the division of otolaryngology-head and neck surgery at the University of Utah Health Care in Salt Lake City. But he said it was “not on my radar screen at all. That’s why I think it’s important: because I’m sure there are many otolaryngologists like myself who are not following this issue.”