And a related study found that babies exposed to secondhand smoke from fathers or other people may be at increased risk of developing weight problems, even if mothers are nonsmokers.
Both studies appear online in advance of publication in the July issue of the journal Pediatrics.
Researchers from the United Kingdom and Brazil, using data on 509 Brazilian and 6,735 British families, say there is reason to believe that mothers who smoke may expose their fetuses to harmful substances that may affect the behavior and conduct of children in later years.
"There was some evidence that maternal smoking in pregnancy is associated with greater conduct/externalizing problems [aggressive behavior, rule-breaking behavior] in the offspring at the age of 4," the authors write.
Mary-Jo Brion, PhD, of the University of Bristol, tells WebMD by email that babies exposed to smoke may be prone to rule breaking, such as lying, cheating, bullying, and disobedience.
Among other conclusions:
- Prenatal smoking by pregnant women may have specific effects on fetal development.
- Maternal smoking seems to be more strongly associated with child problems than is paternal smoking.
- No association was found between maternal smoking and childhood development of attention deficit hyperactivity disorder.
"To some extent it is somewhat surprising that ... maternal smoking may also directly impact child behaviors from exposing the fetus to tobacco in utero," she tells WebMD. "This study suggests that adverse effects on offspring may extend as far as putting children at increased risk of having behavioral problems."
She says the investigators had "complete information" on mothers, fathers, and their children.
Father's Smoking Affects Child's Weight
One of the authors of the second study, Mary Schooling, PhD, of the University of Hong Kong, tells WebMD by email that scientists investigated 6,790 children with nonsmoking mothers, of whom 2,165, or 32%, had fathers who smoked. More than half of the fathers smoked daily and 626 occasionally. And 2,674 children were exposed to secondhand smoke from other sources in infancy or before birth.
In addition, she says, 1,951 children had no exposure to secondhand smoking before or after birth.
The study's key finding, she says, is that paternal smoking clearly seems to be associated with higher childhood weight as assessed by body mass index.
"To protect their children, fathers should avoid smoking from conception onward," she tells WebMD.
The researchers also examined other factors, such as whether children were breastfed after birth.
"The effect of paternal smoking on children's BMI was similar to that of maternal smoking during pregnancy," the authors write.
Among other findings, they report that although paternal smoking was associated with weight as measured by BMI, it was not linked to height of children in their early school years.
A commentary in the July print issue discusses both studies and calls for the promotion of smoking-cessation programs to educate parents on the dangers of exposure to smoke, from the prenatal stage on into the future.
Jonathan P. Winickoff, MD, MPH, of Harvard Medical School, says the conclusion that paternal smoking also may influence "the developmental in utero origins of childhood obesity seems to be a novel finding."
He writes that the two studies "support the need for action to promote tobacco-control activities that would mitigate tobacco exposure throughout childhood development, starting in the prenatal period."
The studies, he writes, "may provide extra motivation to change office practices toward providing tobacco-cessation care."
By Bill Hendrick
Reviewed by Laura Martin
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