Physiology of Glucose Metabolism in Pregnancy
Dietary habits frequently change during pregnancy. Food intake may decrease early in pregnancy because of nausea and vomiting, and food preferences may change later in pregnancy. Several pregnancy-associated hormones also have a major effect on glucose metabolism. Most notable of these is human placental lactogen (hPL), which is produced in abundance by the enlarging placenta. HPL affects both fatty acid and glucose metabolism. It promotes lipolysis with increased levels of circulating free fatty acids and causes a decrease in glucose uptake. In this manner, hPL can be thought of as an anti-insulin. The increasing production of this hormone as pregnancy advances gener-ally requires ongoing changes in insulin therapy to adjust for this effect.
Other hormones that have demonstrated lesser effects include estrogen and progesterone, which interfere with the insulin-glucose relation; and insulinase, which is pro-duced by the placenta and degrades insulin to a limited extent. These effects of pregnancy on glucose metabolism make the management of pregnancy-associated diabetes difficult. DKA, for example, is more common in pregnant patients.
With increased renal blood flow, the simple diffusion of glucose in the glomerulus increases beyond the ability of tubular reabsorption, resulting in the normal glucosuriaof pregnancy, commonly of approximately 300 mg/day.In patients with diabetes, this glucosuria may be much greater, but because of the poor correlation of pregnancy glucosuria values and simultaneous blood glucose concen-trations, using urinary glucose levels is of little value in glucose management during pregnancy.