Schaefer-Graf et al. (1) rightly suggest that the management of women with gestational diabetes mellitus (GDM) should be based on more than glycemic factors alone. However, the study in which they conclude that strict glycemic control is not useful in the absence of the measurements of fetal overgrowth has two unusual features.
The authors’ criteria for diagnosing GDM are lower than those of the World Health Organization or the American Diabetes Association, and they may be including women who could be considered normal. This is supported by the fact that there is little difference between the rate of large-for-gestional-age (LGA) babies in both their groups (12.1% above the 90th percentile) and that of the defining normal population (10%). These women may not have been equally represented in the two groups, as 30% more women in the ultrasound-defined group met their criteria for insulin therapy.
More importantly, the women with larger babies were treated more aggressively. Because their outcome was not different from less aggressively treated women without initially large babies, there is the possibility that the latter might have done better if they had been using the same glycemic targets as the women with large babies. They certainly had higher fasting glucose concentrations, and more of the LGA babies were born to women who did not receive insulin in either group. At the very least, the protocol favors the authors’ hypothesis that insulin intervention before the onset of fetal overgrowth is not helpful.
Jovanovic (2) draws attention to the discrepancy in glucose targets but worries that her own policies, based on strict glycemic control and resulting in a lower macrosomia rate in her GDM population than in the local background population, may have achieved this at the cost of an increase in small-for-gestational-age (SGA) babies. For us, in a clinic of predominantly African and Carribean background, SGA is not an issue. Using Jovanovic’s protocols in women diagnosed by World Health Organization criteria, our SGA rate is <5%. Because SGA is defined as babies in the lowest 10th percentile, our current rate is lower than that of the background population.
Schaefer-Graf et al.’s study supports the use of strict glycemic control in women with demonstrably large babies. This is valuable evidence that such problems may respond to intervention with insulin even after the onset of fetal overgrowth. Reassuringly, none of the differences in the rates of SGA in the study approached significance. We would not, therefore, support the authors’ suggestion that we abandon glycemic indications for insulin therapy in our population until a randomized prospective trial using similarly strict glucose targets in all groups shows that it does more harm than good.