Objectives: Although hyponatremia in preeclamptic patients was previously described, its significance remains unknown. We aimed to describe the prevalence and clinical significance of hyponatremia among a cohort of preeclamptic patients. Methods: An electronic medical record based retrospective cohort study included all singleton deliveries at Hadassah University Medical Center between 2003 and 2015. Preeclampsia, with and without severe features, was defined using the American College of Obstetrics and Gynecology (ACOG) Hypertension in Pregnancy Guidelines. Hyponatremia was defined as a sodium (Na) level ≤130 mEq/L, and severe hyponatremia as <125 mEq/L. A group of normotensive pregnant women, matched for gestational age, gravdity and parity, served as control. Results: A total of 700 preeclamptic patients were identified during the study period. Hyponatremia was noted in 14.6% compared to 0 of 79 patients in the control group. Hyponatremia was strongly correlated with severe features of preeclampsia, adverse neonatal and obstetrical outcome. Severe hyponatremia was strongly correlated with preeclampsia with severe features. Furthermore, even among subgroup of preeclamptic patients without severe features, hyponatremia correlated with less favorable pregnancy outcomes. Conclusions: Among relatively large cohort of preeclamptic patients, hyponatremia was not a rare finding. We found it more common in patients with preeclampsia and severe features. As women with preeclampsia are at risk for hyponatremia, serum sodium levels should be monitored, especially in those with severe features. In preeclamptic patients without severe features, hyponatremia may indicate a need for closer surveillance. However, larger studies are needed to establish hyponatremia as a marker of severity.
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