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Re: The definition of gestational diabetes

Das et al describe an increased neonatal complication rate in both large infants whose mothers were not diagnosed with gestational diabetes, and large infants of gestational diabetics, "diagnosed in accordance to protocol".

The literature on gestational diabetes is inconsistent. How was it defined their study? Many obstetricians still define gestational diabetes as two or more blood glucose values at or over threshold at 0,1 and 2 hours during an oral glucose tolerance test (1,2), after a mother has an initial borderline screen. But this definition was not derived from neonatal outcome data and there is good evidence that only one value at or over threshold increases fetal risk (3,4). Some may classify these mothers as having "impaired glucose tolerance of pregnancy". Others label them as normal. As these infants are at increased risk and treatment has been shown to make a difference, I would diagnose these mothers as having gestational diabetes. It would be interesting to re-examine the Philadelphia data on large infants, reclassify maternal "impaired glucose tolerance" as probable gestational diabetes, and then re-examine the newborn complication rates in the two or three groups.

My own hypothesis is that large infants of mothers who have minimal impairment of glucose tolerance during their pregnancy are mostly normal. However the definition of gestational diabetes needs to be clarified.

Yours truly,

Richard S Taylor MB BS FRCPC Neonatologist, Victoria, BC Canada

Ref: 1. O’Sullivan JB, Mahan CM: Criteria for the oral glucose tolerance test in pregnancy. Diabetes 13:278, 1964

2. Carpenter MW, Coustan DR: Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 144:768–773, 1982

3. Chico A, Lopez-Rodo V, Rodriguez-Vaca D, et al. Features and outcome of pregnancies complicated by impaired glucose tolerance and gestational diabetes diagnosed using different criteria in a Spanish population. Diabetes Res Clin Pract. 2005;68:141-146.