Results of the study were published in the May 8 issue of the New England Journal of Medicine.
The study included more than 23,000 pregnant women from 15 centers in nine countries. None of the women had diabetes. All of the women underwent glucose tolerance testing between 24 and 32 weeks of gestation. This test is performed by first taking a fasting blood sugar reading, then having the woman drink a high-carbohydrate liquid -- in this case a 75-gram carbohydrate drink; 100 grams is standard in the United States -- and then rechecking blood sugar levels at one and two hours to assess how the body is processing the high sugar load.
The higher a woman's blood sugar levels were, the more likely she was to have a C-section, to develop preeclampsia, have premature delivery and to have the delivery complication known as shoulder dystocia, the study found.
Babies born to women with higher glucose levels were more likely to have high insulin levels, low blood sugar, and to have a large birth weight, all indications of exposure to high glucose levels.
The odds of these complications changed continuously as blood sugar levels rose. For example, a woman with the highest levels of blood sugar (but not diabetes) had large babies 26 percent of the time, compared to just 5 percent for women with the lowest blood sugar levels.
"Basically, what they found out is that there is no threshold where you know to treat. That makes it difficult to know what to do with these findings," said Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City.
A second study in the same issue of the journal looked at the use of the oral diabetes medication metformin, versus insulin, the standard treatment for gestational diabetes.
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