A systematic review and meta-analysis of hypocalciuria in pre-eclampsia

Background: Small observational studies have demonstrated that pre-eclampsia is associated with hypocalciuria. Objectives: To compare urinary calcium excretion in pre-eclampsia, gestational hypertension, and chronic hypertension with that in normotensive pregnancies. Search strategy: Online databases were searched through February 2016 using medical subject headings "calcium homeostasis," "calcium excretion," "hypocalciuria," and "pre-eclampsia." Selection criteria: Observational studies were included that evaluated calcium excretion with 24-hour urine collection in patients with pre-eclampsia compared with normotensive pregnant women. Data collection and analysis: Data were extracted from identified studies. The primary outcome was 24-hour urinary calcium excretion. Weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated. Main results: Twenty-one studies were included. Urinary calcium excretion was lower among women with pre-eclampsia than among those with normotensive pregnancies (WMD -158.43, 95% CI -187.95 to -128.92) or chronic hypertension (WMD -92.92, 95% CI -100.55 to -85.29). Excretion was also reduced in severe versus mild pre-eclampsia (WMD -35.00, 95% CI -58.94 to -11.07) and gestational hypertension versus normotensive pregnancies (WMD -50.95, 95% CI -57.74 to -44.17). Calcium excretion was not significantly lower in chronic hypertension versus normotensive pregnancies (WMD -64.45, 95% CI -135.98 to 7.08). Conclusions: Urinary calcium excretion decreases with increasing severity of pregnancy-induced hypertensive disorders, but this trend is not observed in chronic hypertension.