Increased amniotic fluid divalent cation concentration in preeclampsia

Hypocalciuria due to reversibly enhanced tubular calcium reabsorption in preeclampsia has been previously described. As the fetus is exposed in utero to the toxemic environment, its kidney function may be similarly affected. We therefore evaluated the amniotic fluid (AF) concentrations of Ca2+, Mg2+, Zn2+, and Na+ in relation to creatinine in 12 preeclamptic women, 9 pregnant women with chronic hypertension, and 12 control pregnant women. Our data reveal an increased AF Ca2+, Mg2+, and Zn2+ to creatinine ratio in preeclampsia 451 +/- 283; 164 +/- 94; 787 +/- 124 Eq/mol, respectively) as compared with chronic hypertension (256 +/- 141; 94 +/- 46; 504 +/- 124 Eq/mol, respectively), and normal controls (274 +/- 132; 83 +/- 19; 477 +/- 124 Eq/mol, respectively; p < 0.05). Na+ concentration did not vary significantly among the three groups. It is suggested that the higher AF divalent cation concentration in preeclampsia may be due to lower maternal urinary excretion thereby increasing the fetal divalent cation load.