According to the Paediatric and Perinatal Epidemiology study conducted in Japan, exposure to tobacco smoke prenatally and postnatally was associated with hearing impairment in toddlers.

In the study of 50,734 children aged three years, who were born between 2004 and 2010, 3.8 percent were exposed to smoking only during pregnancy; 15.2 percent were exposed in utero to only maternal past smoking; 3.9 percent were exposed only to second-hand smoke at 4 months; and 0.9 percent were exposed to tobacco smoke during pregnancy and at 4 months.

The prevalence of hearing impairment at age 3 years was 4.6 percent. 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 percent increased relative risk of hearing impairment and children exposed to only second-hand smoke at 4 months had a 30 percent increased relative risk.

While, those exposed to only smoking during pregnancy had a 68 percent 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. "Although public health guidelines already discourage smoking during pregnancy and in front of children, some women still smoke during pregnancy and many young children are exposed to second-hand smoke," said senior author Koji Kawakami.

"This study clearly shows that preventing exposure to tobacco smoke during pregnancy and postnatally may reduce the risk of hearing problems in children. The findings remind us of the need to continue strengthening interventions to prevent smoking before and during pregnancy and exposure to second-hand smoke in children", Kawakami continued. The study appears in the journal Paediatric and Perinatal Epidemiology.