Definition of Gestational Diabetes Mellitus (GDM)
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy, regardless of whether insulin or diet modification is used for treatment, and whether or not the condition persists after pregnancy. 1
Core Definitional Elements
The definition applies universally to all cases of glucose intolerance identified during pregnancy, whether the hyperglycemia represents truly new-onset disease or previously unrecognized pre-existing diabetes that is detected through routine pregnancy screening. 1
Treatment modality does not affect the diagnosis: The classification as GDM holds whether the patient requires insulin therapy or achieves glycemic control through diet modification alone. 1
Persistence after pregnancy is irrelevant to the initial diagnosis: The GDM label applies even if glucose intolerance resolves postpartum or if it continues, requiring reclassification later. 1
Important Definitional Limitations
The traditional definition has significant clinical limitations that providers must understand. The severity of hyperglycemia, not simply its presence, determines both short-term and long-term maternal and fetal risks. 1
Many GDM cases represent pre-existing undiagnosed diabetes detected for the first time during pregnancy, since routine screening is not widely performed in nonpregnant individuals of reproductive age. 1
Early pregnancy diabetes (diagnosed before 15 weeks gestation) with glucose ≥126 mg/dL fasting, ≥200 mg/dL random, or HbA1c ≥6.5% should be classified as overt diabetes, not GDM. 2
Epidemiology and Clinical Significance
GDM complicates approximately 7% of all pregnancies in the United States, resulting in more than 200,000 cases annually, though prevalence ranges from 1-14% depending on the population studied and diagnostic criteria employed. 1, 3, 4
GDM represents nearly 90% of all pregnancies complicated by diabetes. 1
The prevalence has increased by 35-100% in recent years, driven largely by the obesity epidemic. 4
Pathophysiology Context
Deterioration of glucose tolerance occurs normally during pregnancy, particularly in the third trimester, with progressive insulin resistance throughout gestation. 3
Women with GDM have insufficient pancreatic beta-cell compensation for the pregnancy-induced insulin resistance, resulting in hyperglycemia. 3