The emergence of the disease concept of Gestational Diabetes Mellitus during the late twentieth century was a product of collaborative efforts between physicians, medical researchers, businesses, and government agencies. This work is fundamentally an institutional history of medicine, situated in three specific genres within the field: disease creation studies, the examination of U.S. public health, and healthcare consumer history. This work traces changes in scientific and medical views, as well as the broader shift in how diseases are defined as that process moved out of the medical clinic and research lab into the halls of policy makers and government agencies. Scientific discovery and understanding emanated from the work of medical researchers, but the post-World War II era in the United States saw government agencies and healthcare businesses gain important roles in defining diseases and in creating consumer identities for patients. This was especially visible with gestational diabetes because many of the women who made up the rising numbers of new cases in the second half of the twentieth century came from lower-income groups who accessed their healthcare through government-subsidized programs like Medicaid. Through a range of historical sources, I examine the development of this dynamic relationship between medical knowledge and practice; business ideologies and approaches in an expanding healthcare market; and government policy on healthcare