In utero exposure to maternal cigarette smoke may be linked with poor performance on reading comprehension tests, according to a new study.
"It's not a little difference - it's a big difference in accuracy and comprehension at a critical time when children are being assessed, and are getting a sense of what it means to be successful," said lead author Dr Jeffrey Gruen of Yale University.
His team 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 she understands what she 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% lower in these areas than classmates born to non-smoking mothers. The difference remained even when researchers took other factors into account, such as if parents read books to their children, worked in lower-paying jobs or were married.
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.
Smoking an attribute
Previous studies have linked smoking during pregnancy 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.
The team, which published their results November 5 in The Journal of Pediatrics, pulled data from more than 5 000 children involved in the Avon Longitudinal Study of Parents and Children (ALSPC) study that began in the early 1990s in the UK. Children with IQ scores below 76 were excluded.
UK researchers collected questionnaires from mothers before and after giving birth - which helps make the self-reported data more trustworthy, said Sam Oh of the University of California, San Francisco, who wasn't involved with the work. If mothers knew their child's reading scores beforehand, they might subconsciously report more or less smoking.
"To me, this study suggests that the effects attributed to in utero smoking can in fact be attributed to the intrauterine environment, and not due to environmental differences that the children grow up in," Oh said.
(Reuters Health, November 2012)
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