Maternal development of gestational diabetes result in fetal macrosomia. The pathophysiology of fetal macrosomia is not very clear but it seems clear that fetal hyperinsulinemia is one driving force. The insulin like growth factor, as well as fibroblast growth factor, also are involved, so a hyperinsulinemic state with increased levels of some growth factors, with increased expression of GLUT proteins in syncytiotrophoblast, may promote excessive fetal growth. It could also be due to elevated levels of maternal free fatty acid which leads to its increased transfer to the fetus accelerating triglyceride synthesis and resulting in adiposity. Ref: Williams Obstetrics 22nd Edition, Page 59, 689 ; Textbook of Obstetrics By D. C Dutta, 6th Edition, Page 286-7