Calciuria in symptom-free primigravid women remote from term: is the response to an oral calcium challenge predictable?

OBJECTIVE: This study was undertaken to compare the calciuric response in symptom-free primigravid women to an oral calcium load between those with normal urinary calcium excretions and those with relatively low urinary calcium excretions. STUDY DESIGN: This was a prospective clinical trial. Eligible primigravid women between 16 and 20 weeks' gestation provided a 24-hour urine sample for determination of urinary calcium/urinary creatinine ratio. On the basis of these results the patients were divided into 2 groups: a relatively hypocalciuric group, in which the urinary calcium excretion was 3.4 mg. kg-1. 24 h-1. All participants undertook a 3-day low calcium dietary regimen. On the fourth day women underwent an oral calcium challenge. A 2-hour urine sample was collected before ingestion of 1 g calcium carbonate (preload). One hour after ingestion the women again collected a 2-hour urine sample (postload). The urinary calcium/urinary creatinine ratios in the preload and postload samples were determined and compared within and between the groups. RESULTS: The mean change (+/-SD) between the preload and postload urinary calcium/urinary creatinine ratios in the relatively hypocalciuric group was 0.60 +/- 1.44 (P =.04); that in the normocalciuric group was 3.09 +/- 2.26 (P =.11 ). There was a 5-fold difference in the response to calcium load between the hypocalciuric women and the normocalciuric women (0.60 vs 3.09), although this difference was not statistically significant (P =.20). CONCLUSIONS: Both hypocalciuric and normocalciuric women responded to an oral calcium challenge by an increase in the calcium excretion. The cause of the hypocalciuria in women at increased risk for preeclampsia is therefore not simply poor absorption of calcium.

Urinary calcium in asymptomatic primigravidas who later developed preeclampsia.

OBJECTIVE: To assess the efficacy of calciuria as a diagnostic test for the prediction of preeclampsia. METHODS: We asked young healthy primigravidas from the prenatal clinic in our hospital to collect a 24-hour urine sample at 17-20 weeks' gestation. Urinary calcium was measured and expressed as calciuria per 24 hours (mg/24 hours), urinary excretion of calcium per 24 hours on a basis of body weight (mg/kg/24 hours), and as the calciuria-creatinuria ratio (mg/mg). For each test, sensitivity, specificity, predictive values, and relative risk (RR) were calculated. The test with the best overall performance was determined by comparing receiver operating characteristic curves. Sixty-nine patients completed the study until the end of the puerperium, and 15 of them were diagnosed with preeclampsia. RESULTS: The most efficient test was the urinary excretion of calcium per 24 hours based on body weight. Using 3.4 mg/kg/24 hours as a cutoff point, we obtained a sensitivity of 80% (95% confidence interval [CI] 59.8-100), specificity 64.8% (95% CI 52.1-77.5), positive predictive value 38.7% (95% CI 21.6-55.8), negative predictive value 92.1% (95% CI 83.5-100), and RR 4.9 (95% CI 1.5-15.8). CONCLUSION: In young, apparently healthy primigravidas, a low urinary excretion of calcium per kilogram of body weight per 24 hours before the end of the first half of gestation is a risk factor for preeclampsia, with an acceptable sensitivity and high negative predictive value, but with a positive predictive value no better than chance.