Gestational diabetes: new criteria may triple the prevalence but effect on outcomes is unclear

Summary box

• Clinical context—Mild gestational diabetes is associated with perinatal morbidity

• Diagnostic change—International recommendation to move from dual step testing to reliance on a single abnormal glucose value in an oral glucose tolerance test with reduced thresholds

• Rationale for change—An observational study showed that any degree of impaired glucose regulation in pregnancy is associated with adverse outcomes

• Leap of faith—Reducing mildly raised blood glucose concentrations will improve outcomes for mother and baby

• Effect on prevalence—Nearly 1 in 5 pregnancies will be identified as being affected by gestational diabetes: a 2-3-fold increase over existing levels of 2-6%

• Evidence of overdiagnosis—Despite increased diagnosis there is no evidence from randomised controlled clinical trials that outcomes are improved

• Harms from overdiagnosis—Many more women will experience medicalisation of their pregnancy with increased intervention

• Limitations—Maternal obesity and excess weight gain in pregnancy are associated with gestational diabetes; both affect birth weight and other more serious pregnancy outcomes. The importance of mild hyperglycaemia is unknown

• Conclusion—We need to understand better how to identify high risk pregnancies, incorporating other important factors in addition to glucose concentration