(RxWiki News) If you're thinking of lighting up while a little one kicks in your tummy, this might stop you. Do you want an overweight child?
The link between obesity and prenatal smoking is not news. But scientists are finding out more about why it exists.
"Pregnant? Don't smoke."
The study, led by Amirreza Haghighi, MD, of the Hospital for Sick Children in Toronto, wanted to find out what the link was between obesity and mothers who smoked while pregnant.
The researchers split a group of 378 adolescents, aged 13 to 19, into two groups. There were 180 whose moms smoked while pregnant, and 198 who were not exposed to smoking while in the womb.
Prenatal exposure to smoking meant the mom smoked more than one cigarette daily during her second trimester.
The unexposed children's moms did not smoke at all for at least a year before becoming pregnant as well as throughout the pregnancy.
The teens were otherwise similar in terms of their gender, age, stage of puberty, height, mother's education and school attendance rates.
The researchers asked the teens what they had eaten in the previous 24 hours to assess how many fat calories they ate typically.
The researchers also measured the body fat percentage of the teens and did scans of their brains with magnetic resonance imaging (MRI).
In the teens' brains, the scientists looked at the parts involving responses to rewards.
They found that the teens exposed to smoking before they were born had about 1.7 kg (3.7 pounds) more body fat on average compared to teens not exposed to prenatal smoking.
This difference remained even after making mathematical adjustments for the children's age, gender and height.
The teens exposed to prenatal smoking also ate about 2.7 percent more fat calories and had a lower amount of volume in their amygdala. The amygdala is one part of the brain involved in reward processing.
The smaller the amygdala in the teens, the more likely they were to eat more fat calories.
These findings led the researchers to conclude that the link between prenatal smoking and obesity may be related to the children preferring to eat more fat due to differences in their brains.
"Prenatal exposure to maternal cigarette smoking may promote obesity by enhancing dietary preference for fat, and this effect may be mediated in part through subtle structural variations in the amygdala," the researchers wrote.
Other differences were also noted between the groups. The children exposed to prenatal smoking weighed less when they were born and were breastfed a shorter length of time.
Even controlling for these differences, however, the teens were still heavier than their unexposed peers.
The study was published September 3 in the Archives of General Psychiatry. The research was funded by the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Quebec and the Canadian Foundation for Innovation. The authors declared no conflicts of interest.