IONIZED MAGNESIUM AND CALCIUM LEVELS IN UMBILICAL-CORD SERUM OF PREGNANT-WOMEN WITH TRANSIENT HYPERTENSION DURING LABOR

Using a new ion selective electrode (ISE) to measure ionized magnesium (IMg2+), we compared levels of IMg2+ with total magnesium (TMg) and s erum ionized calcium levels (ICa2+) in umbilical arterial and venous s erum of 13 parturients who developed transient hypertension in labor w ith levels in 38 who remained normotensive. Ionized, but not total mag nesium levels were significantly lower in the umbilical veins of the h ypertensive compared to the normotensive subjects (0.46 +/- 0.01 v 0.5 1 + 0.01 mmol/L), and these were at least 15% lower than maternal leve ls found in nonpregnant women (0.60 +/- 0.005 mmol/L, P <.001). If umb ilical vein samples reflect maternal levels as well, then these result s suggest that lower IMg2+ levels may play a role in the development o f transient hypertension in labor, and the potential utility of an ion selective electrode for ionized magnesium in the diagnosis of subtle magnesium deficient states.