Gestational diabetes mellitus (GDM) is generally considered to be carbohydrate intolerance with variable severity with onset or first recognition during pregnancy. The concept that pregnancy may bring about alterations of carbohydrate metabolism goes back more than 140 years. In 1882, J. Mathews Duncan described what would later be called GDM, indicating that “diabetes may occur only during pregnancy being absent at other times or may cease with the termination of pregnancy recurring sometime afterwards.” 1 In 1946, Miller observed that perinatal mortality was increased in the previous pregnancies of women with diabetes, 2 and in 1952 Jackson noted a high likelihood of previous stillbirth and fetal macrosomia in women with diabetes. 3 A few years later, Carrington coined the term “gestational diabetes.” 4 In the middle of the twentieth century, one commonly used set of diagnostic criteria for diabetes in the United States was that put forth by the U.S. Public Health Service (USPHS) 5 : a 100 g, 3-hour oral glucose tolerance test (OGTT) was administered. Diabetes was diagnosed if both the fasting and 3-hour whole blood glucose values were ≥130 mg/dL or if one of these two was elevated and, in addition, either the 1-hour value was ≥195 mg/dL or the 2-hour value was ≥140 mg/dL.