Decreased Ionized Calcium and Increased Parathyroid Hormone in the Serum of Mild Gestational Hypertensive Patients at the Third Trimester: A Link Between Calcium Metabolism and Hypertension in Pregnancy

Since calcium intake is inversely related to the risk of gestational hypertension and calcium supplementation reduces vascular sensitivity to angiotensin II, we determined by a specific electrode serum ionized calcium and calcium regulating hormones by radioassay in a French Caucasian population. During the third trimester of gestation we observed a significant decrease in ionized serum calcium in 22 mild to moderate hypertensive pregnant women without proteinuria compared to 15 normotensive pregnant control subjects (p<0.01). We also observed in this group elevated intact serum PTH and significant elevated carboxyterminal serum PTH within the nonpregnant normal range (p<0.05), but calcitonin and 1,25-dihydroxycnolecalciferol remained unchanged. It appears that activation of the parathyroid glands is secondary to the decrease of ionized serum calcium which may result from a general cellular defect in cationic exchange. The importance of these observations in the pathogenesis of gestational hypertensive disorders remains to be delineated.