Babies born to mothers who smoke more than a pack of cigarettes a day while pregnant have lower reading scores and a harder time with reading tests, compared with children whose mothers do not smoke.

This is the conclusion of a recent study conducted by researchers at Yale School of Medicine and published in The Journal of Pediatrics in November 2012. The reading tests measured how well children read out loud and understood what they were reading.

This isn’t the first study to suggest that smoking in pregnancy may affect a child’s future health and development. A study released in August 2012 said that smoking during pregnancy increases a child’s risk of asthma. In addition, a 2009 study linked smoking during pregnancy to behavioral problems among 3 and 4 year olds boys.

Jeffrey Gruen, M.D., professor of pediatrics and genetics at Yale and his team examined data from over 5,000 kids enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC), which is an extensive trial of 15,211 kids from the years 1990 to 1992 at the University of Bristol in the U.K.

The experts compared 7 different areas with smoking during pregnancy:

  • single-word identification
  • reading speed
  • spelling
  • accuracy
  • reading comprehension
  • real reading
  • non-word reading

The researchers adjusted for socioeconomic status, how the mother and child interacted with one another, and 14 other impacting factors.

Experts discovered through their experiments that the children whose mothers smoked at least one pack a day while pregnant, had reading scores that were 21% lower than the children whose mothers did not smoke while pregnant. The reading tests were given to the kids when they were 7 years old, and again when they were 9.

On average, kids who were born to mothers who smoked during pregnancy were ranked 7 spots lower in terms of reading accuracy and capability to comprehend reading material than their classmates whose mothers did not smoke.

Gruen said, “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.”

He notes that the impact of smoking during pregnancy is stronger when kids fall short in other phonological areas, such as speech, which indicates a link between smoking and phonological capability.

Gruen continued:

The interaction between nicotine exposure and phonology suggests a significant gene-by-environment interaction, making children with an underlying phonological deficit particularly vulnerable.”