Maternal and neonatal outcomes according to the timing of diagnosis of gestational diabetes: A critical appraisal.

Gestational diabetes mellitus (GDM) is the most common metabolic abnormality of pregnancy and is associated with early and late adverse outcomes for both mothers and fetuses. Conventionally, GDM is diagnosed between 24 and 28 gestational weeks (GW) (late-onset GDM). With the increasing prevalence of prediabetes among women of reproductive age, GDM is increasingly being diagnosed before 24 GW in high-risk populations (early-onset GDM). Compared with late-onset GDM pregnancies, early-onset GDM pregnancies are at greater risk for neonatal adverse events, such as perinatal mortality, neonatal hypoglycemia, neonatal respiratory distress syndrome, and macrosomia. The TOBOGM study revealed that the initiation of treatment before 20 GW can modestly reduce composite neonatal outcomes, mainly due to a reduction in the rate of neonatal respiratory distress syndrome. The benefit was greater when treatment was initiated before 14 GW. The probable mechanisms for early-onset hyperglycemia-induced neonatal adverse events are decidual and placental defects, interference with fetal lung development, and fetal glucose steal. There is no international consensus on the GDM screening strategy in early pregnancy, and its cost-effectiveness is questioned by several professional bodies. Further prospective randomized controlled studies are strongly recommended to alleviate confusion in clinical practice regarding the management of mild hyperglycemia in early pregnancy.