The findings suggest a potential explanation for the link between smoking during pregnancy and health complications in children. (Representational Image)
Mothers-to-be, take note! Smoking cigarettes during pregnancy may chemically modify the DNA of the baby, mirroring patterns seen in adult tobacco users, according to a new study of over 6,000 newborns and their mothers around the world.
The researchers also identified new development-related genes affected by smoking.
The findings from one of the largest studies of its kind suggest a potential explanation for the link between smoking during pregnancy and health complications in children.
"I find it kind of amazing when we see these epigenetic signals in newborns, from in utero exposure, lighting up the same genes as an adult's own cigarette smoking. There's a lot of overlap," said Stephanie London, from the US National Institute of Environmental Health Sciences (NIEHS).
"This is a blood-borne exposure to smoking - the foetus isn't breathing it, but many of the same things are going to be passing through the placenta," London said.
Links between smoking and chemical modifications to DNA, or methylation, have been found for developing foetuses in smaller studies, but the larger analysis gives scientists more power to uncover patterns.
An international team of researchers pooled results from 6,685 newborns and their mothers around the world. Based on questionnaires, mothers were labelled as "sustained smokers" who smoked cigarettes daily throughout most of pregnancy (13 per cent), "non-smokers" (62 per cent), or those with "any smoking" during pregnancy (25 per cent), which captured mothers who were occasional smokers or who quit smoking early on.
To analyse methylation in the newborns' DNA, researchers collected samples mainly from blood in the umbilical cord after delivery.
For the newborns whose mothers fell into the "sustained smoker" category, the research teams identified 6,073 places where the DNA was chemically modified differently than in the "no smoking" newborns.
About half of these locations could be tied to a specific gene.
Researchers found that this collection of genes related to lung and nervous system development, smoking-related cancers, birth defects such as cleft lip and palate, and more. In a separate analysis, many of these DNA modifications were still apparent in older children whose mothers had smoked during pregnancy.
Next steps include building on the preliminary gene-expression analyses conducted by the research team to better understand how these DNA modifications might influence child development and disease.
"We already knew that smoking is related to cleft lip and palate, but we don't know why. Methylation might be somehow involved in the process," London said.
The study was published in the American Journal of Human Genetics.