Using a new ion selective electrode (ISE) to measure ionized magnesium (IMg2+), we compared levels of IMg2+ with total magnesium (TMg) and serum ionized calcium levels (ICa2+) in umbilical arterial and venous serum of 13 parturients who developed transient hypertension in labor with levels in 38 who remained normotensive. Ionized, but not total magnesium levels were significantly lower in the umbilical veins of the hypertensive compared to the normotensive subjects (0.46 +/- 0.01 v 0.51 +/- 0.01 mmol/L), and these were at least 15% lower than maternal levels found in nonpregnant women (0.60 +/- 0.005 mmol/L, P < .001). If umbilical vein samples reflect maternal levels as well, then these results suggest that lower IMg2+ levels may play a role in the development of transient hypertension in labor, and the potential utility of an ion selective electrode for ionized magnesium in the diagnosis of subtle magnesium deficient states.
Calcium Female