Research has revealed the epigenetic effect of a mother’s smoking on their unborn child.

A study of over 6,000 mothers and their newborn children shows that smoking cigarettes while pregnant chemically modifies a foetus’ DNA, in similar ways to the effects on adult smokers.

The researchers also identify new development-related genes affected by smoking, adding more weight to 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,” says co-senior author Stephanie London, an epidemiologist and physician at the UK’s National Institutes of Health.

“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.”

The study was a large meta-analysis, pooling results from previous studies involving 6,685 newborns and their mothers around the world.

Researchers collected samples mainly from blood in the umbilical cord after delivery to analyse methylation in the newborns' DNA.

Of the newborns the 13 per cent whose mothers fell into the “sustained smoker” category, the research teams identified 6,073 places where the DNA was chemically modified differently than the 62 per cent in the “no smoking” newborns.

About half of these locations could be tied to a specific gene.

The team 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.

“Many signals tied into developmental pathways,” says Bonnie Joubert, an epidemiologist at the NIEHS and a co-first author on the paper.

In a separate analysis, many of these DNA modifications were still apparent in older children whose mothers had smoked during pregnancy.

Expert will now use the preliminary gene-expression analyses to better understand how these DNA modifications might influence child development and disease.

For example, London says, “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”.

The study also marks the first paper from the international Pregnancy and Childhood Epigenetics (PACE) consortium, which is applying the “consortium approach” to studies that brings large teams of scientists together to tackle tough questions.

PACE is looking at questions about the impact of a mother's body weight, alcohol intake, and air pollution on her child’s epigenetic marks, and the effects of those marks on the child's health.

The full study is accessible here.