Mothers who smoke during pregnancy may be putting their children at risk for having poor reading skills, say researchers.
They explain that in a group of students who come from similar backgrounds and have a comparable level of education, their results translate to a child whose mother smoked during pregnancy being ranked seven places lower for reading accuracy and comprehension skills than a child of a nonsmoker in a class of 31 children.
"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 investigator Jeffrey Gruen (Yale School of Medicine, New Haven, Connecticut, USA) in a press statement.
Gruen and colleagues assessed the impact of high (above 17 mg/day), low (below 17 mg/day), and no prenatal exposure to nicotine in a group of 5119 7-9-year-old school children from the UK who were participating in the Avon Longitudinal Study of Parents and Children in terms of reading skills (speed, fluency, accuracy, spelling, and comprehension).
Level of nicotine exposure was calculated using maternal self-report at 8-42 weeks pregnancy and by multiplying the number of cigarettes smoked per day with the nicotine content of each brand.
Following adjustment for confounders such as gender, ethnicity, gestational age, and mother's marital status, the researchers found that children with the highest prenatal exposure to nicotine had the lowest average values across all the reading outcomes tested except for nonword reading.
Notably, the interaction between prenatal nicotine exposure and reading skills was significantly influenced by phonology score - a marker of speech ability - such that children with the lowest phonology scores and highest nicotine exposure had the lowest scores on the reading skills test.
"The interaction between nicotine exposure and phonology suggests a significant gene-by-environment interaction, making children with an underlying phonological deficit particularly vulnerable," commented Gruen.
The results of this study are published in the Journal of Pediatrics.
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