Evidence for early treatment of hyperglycemia in pregnancy

Gestational diabetes mellitus (GDM) is conventionally diagnosed at 24-28 weeks' gestation, corresponding to a period of increasing pregnancy-related insulin resistance. However, glucose intolerance may be present earlier in pregnancy, preceding standard screening and not meeting criteria for overt pre-existing diabetes. Observational studies suggest that even mild hyperglycaemia in early pregnancy is associated with adverse maternal and neonatal outcomes, raising questions regarding the clinical benefits of early diagnosis and treatment. This review distinguishes conventional GDM from early-pregnancy hyperglycaemia, summarising current diagnostic frameworks and the physiological mechanisms underlying dysglycaemia in early gestation. We examine mechanistic and epidemiological data linking early maternal hyperglycaemia to maternal and foetal outcomes and review glycaemic thresholds associated with adverse outcomes. Despite biological plausibility, randomised controlled trials and meta-analyses to date have not demonstrated consistent improvements in major maternal or neonatal outcomes with early diagnosis and treatment. Important limitations of the existing evidence base and priorities for future research are highlighted.