Women who drink a lot of sweet sodas during pregnancy may be more likely to give birth prematurely, a new study suggests.
The study, of more than 60,000 pregnant women in Norway, found that those who drank one sugary soda a day were up to 25 percent more likely to give birth prematurely than those who avoided the sweetened drinks.
However, it's not clear whether the drinks themselves are to blame for the early births.
"We are all desperately searching for causes of preterm birth," said Dr. Michael Katz at the New York-based March of Dimes foundation, a non-profit organization that works to improve babies' health. But, added Katz, who was not involved in the study, "this study does not indicate that (drinking soda) is a tremendously serious risk of any sort."
What women eat during pregnancy has come under scrutiny in recent years. Studies have suggested that a host of different foods, from fish to caffeine, could affect pregnancy outcomes, including premature birth.
In the US, about 1 in every 8 babies is born prematurely, before 37 weeks' gestation, according to the Centers for Disease Control and Prevention. Those that survive may have neurological problems, or poor vision and hearing.
Previous research in Denmark suggests that drinking artificially sweetened soda increases the risk of preterm birth.
So Dr. Linda Englund-Ögge, who led the research at Sahlgrenska University Hospital in Gothenberg, Sweden, wanted to see if her team would find the same effect in Norwegian women.
They looked at data on 60,761 Norwegian women who participated in a large-scale survey on mother and child health done between 1999 and 2008. The women answered questions on lifestyle, health and nutrition, including how many sweetened sodas they drank, at weeks 15, 22 and 30 of their pregnancy,
During the ten-year study, 3281 babies were born prematurely - about 5.4 percent of births. Researchers found that those births were strongly associated with women who had a high intake of sugary drinks.
Women who drank more than one sugar sweetened drink in a day increased their chances of delivering early by 25 percent over those who never drank sugary drinks.
Those who drank artificially sweetened sodas on a daily basis were 11 percent more likely to give birth prematurely than those who never drank the sweet beverages.
Body weight also seemed to be a factor, with the strongest association between preterm birth and sugary drinks seen among overweight women.
Those who drank at least one sugary soda a week were 30 percent more likely to deliver preterm than overweight women who never drank sodas. The risk increased by 41 percent if they drank soda every day.
However, the new findings, published in the American Journal of Clinical Nutrition, cannot prove that sugary drinks cause preterm births. Lifestyle and other factors that go along with high sugar consumption may also play a role.
Nutrition, maternal age, smoking, alcohol, obesity, chronic health problems like diabetes, and genetic conditions, have all been implicated in preterm birth.
The authors note in their report that women who drank the most sweetened drinks were also more likely to smoke, eat more calories, and have a higher body mass index (BMI) - a measure of weight relative to height - than those who drank fewer sugary drinks.
But for now, Englund-Ögge and her colleagues can only speculate on the causes of the link between the sugary beverages and preterm births.
"What we think is that those women who have a high intake of both (types of soda) might have another dietary pattern than those who say they don't drink either of those beverages," Englund-Ögge told Reuters Health.
Previous research suggests that breakdown products of the sweetener aspartame could play a role in premature birth. High levels of the sugar glucose in women who eat a lot of sugar have also been implicated.
"We don't want to say that pregnant women shouldn't drink sugary or artificially sweetened drinks," said Englund-Ögge. But women should try to cut down on sugar and eat more fruit and vegetables when they are pregnant, she added.
Katz agreed that the study should not be a cause of anxiety, but if women are concerned they should avoid drinking sweetened drinks. "Water is an excellent thirst quencher," he said.