Ionized serum magnesium and potassium levels in pregnant women with preeclampsia and eclampsia.

A prospective, cross-sectional study was performed to determine whether patients with preeclampsia or eclampsia had difficult serum levels or fractions of the active, ionized form of magnesium (IMg2+) as compared to normal, pregnant women. Using a novel ion selective electrode, we determined the IMg2+ levels and fractions as well as ionized calcium, sodium and potassium (K) in venous serum drawn on admission from 33 normal, pregnant women; 12 women with preeclampsia; and 2 women with postpartum eclampsia. Levels in 42 nonpregnant, age-matched, healthy women were also measured. We found that in normal pregnancy, levels and fractions of IMg2+ were significantly decreased as compared to levels and fractions in nonpregnant women (0.48 +/- 0.01 [SE] versus 0.60 +/- 0.005 mmol/L, and 63.2 +/- 1.0% versus 71.6 +/- 0.6%; P < .001 for both), but the levels and fractions in preeclamptics (0.48 +/- 0.01 mmol/L and 64.2 +/- 1.7%) were not significantly different (P > .05) from those in normal, pregnant women. Similarly, the levels and fractions of IMg2+ in the two eclamptic patients were within the ranges of normal and preeclamptic pregnancies. When the other cations were analyzed, a highly significant elevation (P < .001) in the mean K+ level and the K+/IMg2+ ratio in the preeclamptic patients was noted. Thus, it appears that serum IMg2+ levels are maintained in preeclampsia and eclampsia, but disturbances in K homeostasis and in the interrelationships between K and IMg2+ may occur.