Glucose ingestion and whole blood ionized calcium and magnesium in the third trimester of pregnancy.

OBJECTIVE To test the hypothesis that glucose ingestion leads to a decrease in plasma ionized calcium (iCa) and ionized magnesium (iMg) during the third trimester of pregnancy. METHODS We studied 54 women who underwent a 50 g glucose challenge test (GCT) and 27 women who underwent a 3-hour 100 g glucose tolerance test (GTT) because of an abnormal GCT. Plasma glucose was measured with an automated chemistry analyzer, while whole blood iCa and iMg were measured using an ion-selective electrode. RESULTS The 1-hour plasma glucose post-GCT correlated inversely with whole blood iCa (r = -0.322, p = 0.027). The 3-hour plasma glucose GTT revealed a similar, but not statistically significant, decrease in blood iCa (r = -0.378, p = 0.356). The combined 1-hour peak plasma glucose during GTT and GCT correlated inversely with iCa (r = -0.376, p = 0.001), but not with iMg (r = 0.050, p = 0.737). Using multiple regression with iCa as the dependent variable and plasma glucose and glucose dose (50 or 100 g) as independent variables, both plasma glucose and glucose dose were inversely correlated with iCa (R2 = 0.45, p < 0.001). CONCLUSION We conclude that in pregnancy, induced hyperglycemia correlates with a drop in blood iCa concentrations; however a 100 g glucose load leads to a lesser iCa decrease than a 50 g load.