Smoking during pregnancy is well known to harm developing fetuses, increasing babies' risk of birth defects and even death, and making children more likely to develop health problems throughout childhood.

A new study suggests another worrisome outcome — women who smoke during pregnancy significantly increase their daughters' risk of developing both obesity and gestational diabetes, a type of diabetes that causes high blood sugar during pregnancy.

The results, published in the journal Diabetologia, are among the few that link smoking during pregnancy to negative outcomes that last into adulthood, say the researchers.

Researchers at Lund University in Sweden and the U.S. National Institutes of Health (NIH) analyzed data from the Swedish Medical Birth Register in order to investigate how often women developed diabetes and obesity if their mothers smoked during pregnancy.

In a sample of women who were born in or after 1982, the year when maternal smoking data was first collected in Sweden, the researchers analyzed data from over 80,000 pregnancies.

The pregnant women were categorized into three groups according to their mothers' smoking habits: non-smokers, moderate smokers, and heavy smokers who had more than nine cigarettes per day.

The researchers found that 7,300 of the pregnant women had become obese in adulthood, and 291 of them developed gestational diabetes while pregnant.

Women who were moderately exposed to smoking had a 36 percent higher risk of obesity, while those who were heavily exposed had a 58 percent higher risk.

Women whose mothers smoked moderately while pregnant with them had a 62 percent higher risk of gestational diabetes than those born to non-smokers, and interestingly, the ones whose mothers smoked heavily only had a 52 percent higher risk.

Both associations held up after the researchers controlled for other factors including age, body-mass index, and birth weight.

How Could Smoking During Pregnancy Cause Obesity in Offspring?

It's unclear what causes the association between smoking and risk for gestational diabetes and obesity, but the researchers suggest shifts in biological mechanisms that regulate appetite and feelings of fullness.

Previous studies have shown that prenatal nicotine exposure causes a decrease in insulin-producing cells in the pancreas, as well as an increase in fat cell production, which predispose offspring to diabetes and obesity, respectively.

Other research suggests that the offspring of smoking mothers show epigenetic changes, which are alterations to the way that genes are expressed, that make them more likely to develop obesity or diabetes.

The researchers admit that they may have missed some relevant factors that might have accounted for the differences between the offspring of smoking and nonsmoking mothers. Socioeconomic health markers like education level and income, for example, were not included in the Swedish Medical Birth Register data.

Still, they believe the results are conclusive enough to identify a link between mothers' nicotine use and their offspring's predisposition to gestational diabetes, and to reiterate the dangers of smoking during pregnancy.

"Although short-term detrimental effects of smoking on the individual and her offspring are well known," they wrote, "such associations might extend into adulthood, making the incentive stronger for undertaking preventable measures, particularly as numbers in some countries point to an increase in daily smoking among young women."

According to the U.S. Centers for Disease Control and Prevention (CDC), about 13 percent of women in the United States reported smoking in their last trimester of pregnancy in 2008. Another study from last year revealed that over a fifth of white American women in a large sample smoked during pregnancy.

Source: Mattsson K, Källén K, Longnecker M P, Rignell-Hydbom A, Rylander A. Maternal smoking during pregnancy and daughters' risk of gestational diabetes and obesity. Diabetologia, 2013.