Children whose mothers smoked during pregnancy are more likely to be overweight than those who did not, according to researchers.
A study by Aberdeen University compared the Body Mass Index (BMI) of siblings at five-years-old whose mothers smoked in-between pregnancies.
It found those exposed to smoke in the womb had a higher BMI than the older sibling who had not.
Dr Steve Turner, who led the research, said: "This study looked at the relationship between maternal smoking and childhood obesity.
"Previous studies have identified a link between the two but saying that one causes the other is problematic because there are lots of other factors that might explain this relationship, for example people from a poor communities are known to smoke more than those in more affluent communities.
"Also, children in those communities tend to be more obese so it may be that the relationship between smoking and obesity is actually explained by socioeconomic status."
The relationship between pregnant mothers who smoke and childhood obesity has been identified in previous studies, but on this occasion it compared the effect of maternal smoking on siblings.
The results, published in the journal Paediatric and Paediatric Epidemiology, found if the mother started smoking between pregnancies, the younger child had increased BMI compared to their older unexposed brother or sister.
"This study adds to the huge body of evidence that maternal smoking in pregnancy is harmful and the harm isn't just limited to the pregnancy itself - it lasts well-beyond the pregnancy," Dr Turner said.