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231PART III. Pregnancy Complicated by Gestational Diabetes Mellitus1/13/15 9:45 2321/13/15 9:45 of Waters, Catalano, MD21The world isn’t just the way it is. It is how we understand it. .And in understanding something, we bring something to it .—Yann Martel (Life of Pi)Key Points.•. Normal Pregnancy is characterized by a 40%–50% decrease in peripheral (skeletal muscle) and endogenous () insulin sensitivity; as a result there is a two- to threefold increase in insulin secretion and insulin clearance –30%.•. Gestational diabetes mellitus (GDM) is characterized by inadequate pancreatic β-cell response for the increased level resistance present in women with GDM as compared with a matched control group.•. Women with GDM have approximately 50% less total insulin secretion in comparison to non-GDM diabetes (GDM) is the most common type of diabetes identified during pregnancy, affecting 3%–7% of all –3 For any gravida, the natural increase in insulin subsequent increasing postprandial glucose levels, a “diabetogenic state.” In a pregnancy not GDM, the increase in insulin resistance is met by an insulin production to maintain a euglycemic In contrast,.women who develop GDM can have a suboptimal insulin response.(a failure of the pancreatic β-cell to compensate for the increasing insulin resistance), a decrease in peripheral and central , or a mix of Although primarily a disorder metabolism, GDM affects all aspects of maternal . However, the basic pathophysiology of GDM can by describing the changes that lead to a deviation normal glucose homeostasis of pregnancy. This review the metabolic imbalances that characterize GDM, both of the insulin secretion/sensitivity relationship and disturbances in the rhythms of glucose HOMEOSTASIS/NORMAL homeostasis involves a complex relationship glucose concentration (G), insulin response (I), sensitivity (IS), hepatic glucose production (HGP), clearance (IC). Glucose is absorbed via on the apical membrane of the intestine against concentration gradient. Subsequent efflux is facilitated transporters on the basement membrane of the 233Both the density of the transporters and the sodium gradient the uptake regulate the transport of glucose. Within the , glucose concentration is a result of placental facilitated diffusion transporters solely and is then regulated by the concentration gradient and fetal glucose transporters (GLUT) several types that vary in their kinetic properties, and localization, with at least five subtypes important . GLUT1 is present in placenta, muscle, adipose tissue,.brain, and endothelium and is involved in cellular metabolismPresent within the syncytiotrophoblast and on the basal membranes, GLUT1s are the primary transporter of glucose to the GLUT2 is present on pancreatic β-cells, liver,.small intestine, and renal proximal tubules and acts as a and fructose transporter. GLUT3 is present in neural the small intestines and acts as a scavenger under which G is low and in high demand due to increased metabolism. GLUT4 is expressed only in insulin-responsive tissue muscle, heart, and adipose tissue. Finally, GLUT5 is a found in the small intestine, brain, muscle, and adipose glucose metabolism primarily takes place muscles requiring the GL

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