Babies exposed to their mother's cigarette smoke in the womb later perform more poorly on reading comprehension tests, according to a new study.
In the study, researchers found that children born to mothers who smoked more than one pack per day struggled on tests specifically designed to measure how accurately a child reads aloud and if the child understands what they read.
On average, children exposed to high levels of nicotine in utero -- defined as the minimum amount in one pack of cigarettes per day -- scored 21 per cent lower in these areas than classmates born to non-smoking mothers. The difference remained even when researchers took other factors -- such as if parents read books to their children, worked in lower-paying jobs or were married -- into account.
Put another way, among students who share similar backgrounds and education, a child of a smoking mother will on average be ranked seven places lower in a class of 31 in reading accuracy and comprehension ability, said co-author Jan Frijters of Brock University in Ontario, Canada.
Previous studies have found smoking during pregnancy is linked to lower IQ scores and academic achievement, and more behavioural disorders. The authors found no reports so far that zeroed in on specific reading tasks like accuracy and comprehension in a large population.