Researcher Matthew Longnecker of the National Institutes of Health found the association in data on women in Sweden, where medical records note whether women smoked when they were pregnant.
In addition, Longnecker found if the daughters of mothers who smoked become pregnant, they had a higher risk of pregnancy-related -- gestational -- diabetes.
"Daughters of mothers who smoked while pregnant had about a 50 percent increase in risk of obesity and gestational diabetes," Longnecker said in a statement.
Longnecker speculated chemicals in tobacco products might make developing fetal cells more likely to become large fat cells, and this might permanently damage the developing pancreas, which makes insulin.
The study was published in the journal Diabetologia.