As per etiological classification of diabetes mellitus, Gestational diabetes mellitus is

Etiologic Classification of Diabetes MellitusI. Type 1 diabetes (beta cell destruction, usually leading to absolute insulin deficiency)Immune-mediatedIdiopathicII. Type 2 diabetes (may range from predominantly insulin resistance with relative insulin deficiency to a predominantly insulin secretory defect with insulin resistance)III. Other specific types of diabetesGenetic defects of beta cell development or function characterized by mutations in:Genetic defects in insulin actionDiseases of the exocrine pancreas--pancreatitis, pancreatectomy, neoplasia, cystic fibrosis, hemochromatosis, fibrocalculous pancreatopathy, mutations in carboxyl ester lipaseEndocrinopathies--acromegaly, Cushing's syndrome, glucagonoma, pheochromocytoma, hypehyroidism, somatostatinoma, aldosteronomaDrug- or chemical-induced- Glucocoicoids, vacor (a rodenticide), pentamidine, nicotinic acid, diazoxide, b-adrenergic agonists, thiazides, calcineurin and mTOR inhibitors, hydantoins, asparaginase, a-interferon, protease inhibitors, antipsychotics (atypicals and others), epinephrineInfections--ongenital rubella, cytomegalovirus, coxsackievirusUncommon forms of immune-mediated diabetes--"stiff-person" syndrome, anti-insulin receptor antibodiesOther genetic syndromes sometimes associated with diabetes--IV. Gestational diabetes mellitus (GDM)Ref: Harrison 19e pg: 2399