Most of the guidelines for diagnosing gestational diabetes are derived from studies that link blood glucose levels during pregnancy to a mother’s risk of developing type 2 diabetes in the future. But what about the baby? A new large international study has demonstrated that maternal blood glucose during pregnancy can affect fetuses even at levels usually considered normal.

Boyd Metzger, MD, a professor at Northwestern University, and his colleagues tracked statistics on birth weight, hypoglycemia (low blood glucose) at birth, Caesarian sections, and C-peptide levels (a proxy for insulin secretion). They also looked at more serious outcomes like birth injuries. All of these measures were found to correlate with increasing maternal glucose levels, and at levels previously considered normal and healthy, well below the established diabetic threshold.

“For a long time, there’s been a lot of controversy about what level of blood sugar is important … from the perspective of the baby,” says Metzger. “Now we have data, very strong data. But, it’s not easy to move to the next step.” Without a break point, it will be a challenge for patients and doctors to decide at what level treatment is appropriate. An international group of researchers is currently discussing the implications of the study for diagnostic and treatment guidelines.

This study was published in the May 8, 2008, issue of the New England Journal of Medicine.