Exposure to tobacco smoke prenatally and postnatally was associated with hearing impairment in a Paediatric and Perinatal Epidemiology study of young children in Japan.
In the study of 50,734 children aged 3 years who were born between 2004 and 2010, 3.8% were exposed to smoking only during pregnancy; 15.2% were exposed in utero to only maternal past smoking; 3.9% were exposed only to second-hand smoke at 4 months; and 0.9% were exposed to tobacco smoke during pregnancy and at 4 months.
The prevalence of hearing impairment at age 3 years was 4.6%. Compared with children not exposed to tobacco smoke prenatally and at 4 months, children exposed to only maternal past smoking during pregnancy had a 26% increased relative risk of hearing impairment, children exposed to only second-hand smoke at 4 months had a 30% increased relative risk, those exposed to only smoking during pregnancy had a 68% increased relative risk, and those exposed to smoking during pregnancy and second-hand smoke at 4 months had a 2.4-times increased relative risk.
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