WEDNESDAY, May 7 (HealthDay News) -- Women with high blood sugar levels during pregnancy face an increased risk of complications, even if the high blood sugar readings don't meet the criteria for gestational diabetes.

In a large, international study, researchers found that for each standard deviation increase in blood sugar, there was a greater risk of complications, such as having a large birth weight baby or needing a Caesarean section delivery.

"We found strong independent associations between a mother's blood sugar levels during an oral glucose tolerance test and 28 weeks of gestation and the pregnancy outcomes," said the study's lead author, Dr. Boyd Metzger, the Tom D. Spies professor of metabolism and nutrition at the Feinberg School of Medicine at Northwestern University in Chicago.

What this means for pregnant women right now, however, isn't clear.

"Because the relationship between the mother's blood glucose level and risk tend to be continuous and linear, it is not clear where the risk reaches the point where treatment should optimally begin," said Metzger.

"We were hoping there would be a breakpoint," explained another of the study's authors, Dr. Don Coustan, professor and chair of obstetrics and gynecology at the Warren Alpert Medical School of Brown University in Providence, R.I. "But, the relationship between glucose levels and outcomes were continuous, which means it will be difficult to decide where to put the 'treating' point."

Coustan added that there will be a conference in June where pregnancy and diabetes experts will likely debate the pros and cons of treating hyperglycemia. For now, he said, he suspects that "doctors will still use the glucose threshold they're currently using."

One thing that was clear from the study is that higher odds of complications, like an increased risk of C-section or a large baby, are related to high blood sugar and not to other conditions, such as obesity or older maternal age, according to Metzger.

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. The study included 751 women, randomly assigned to receive metformin or insulin treatment.

The researchers found that metformin was well-tolerated, although almost 43 percent of the women eventually required the use of supplemental insulin. There were no serious adverse events reported for mother or baby from the use of metformin, according to the study.

Of this study, Zonszein said, "My guess is that until we have larger studies, there's not going to be a big change in recommendations, because we have so much experience with insulin." But, he added, many women and obstetricians may welcome these findings because "giving a pill is easier than giving insulin." He said another oral medication, glyburide, was also found effective in another small trial.

More information

To learn more about gestational diabetes, visit the American Diabetes Association.