Proposed new diagnostic criteria for gestational diabetes--a pause for thought?

New criteria for the diagnosis of gestational diabetes promulgated by the International Association of Diabetes and Pregnancy Study Groups (IADSPG) have been adopted by a number of groups, including the American Diabetes Association. These criteria will increase two- to three-fold the number of women diagnosed with gestational diabetes and have enormous resource implications. The recommendations are derived from observations made in the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study, which demonstrated continuous relationships between maternal glucose tolerance and two clinically relevant outcomes of pregnancy (caesarean section rate and neonatal hypoglycaemia) and two surrogate measures (birth weight and cord C-peptide). The recent randomized intervention studies in mild gestational diabetes indicate that the major effects of detecting and treating mild gestational diabetes are a reduction in mean birthweight of 100-140 g, and a reduction in the incidence of shoulder dystocia. However, the women included in these studies were identified using different diagnostic criteria, and it cannot be assumed that women diagnosed by the less stringent IADSPG criteria will have the same benefit. Moreover, as the majority of cases of macrosomia and shoulder dystocia occur in women with normal glucose tolerance, the real impact of diagnosing many more 'cases' of gestational diabetes is likely to be minimal. The concentration on mild degrees of hyperglycaemia may well be misplaced, as most of the outcomes usually attributed to gestational diabetes are more strongly associated with maternal obesity and weight gain in pregnancy. The new testing procedure (with diagnosis based on a single blood glucose measurement) will inevitably be imprecise. Given the many reservations about the new criteria an urgent but dispassionate debate is required on the risks, costs and benefits of their introduction.