Calcium and Calciotropic Hormones in Transient Hypertension of Pregnancy Versus Preeclampsia

Abstract

Objective: Women with preeclampsia (PE) have markedly reduced urinary calcium excretion compared to normotensive, pregnant controls (NT). This abnormality in PE is accompanied by significandy reduced serum ionized calcium, increased parathyroid hormone, and reduced 1,25(OH)₂-vitamin D levels. Urinary calcium in women with transient hypertension of pregnancy (THP) may be normal, but serum calcium and calciotropic hormones have never been reported. We set out to determine whether calcium and calciotropic hormones differed between women with THP and PE.

Methods: Third-trimester women with THP were studied and compared to values previously reported but concurrently measured for NT and PE. Urinary calcium, sodium, creatinine, and protein in conjunction with serum total and ionized calcium, intact parathyroid hormone (PTH), 25(OH)-vitamin D, 1,25(OH)₂-vitamin D, and phosphate were measured in these women.

Major Outcome Measure: Our hypothesis was that women with PE and THP could be distinguished on the basis of urine and serum calcium and calciotropic hormones.

Results: Urinary calcium excretion in women with THP was remarkably similar to women with NT but significantly higher than women with PE (6.6 1.3 vs. 6.5 0.7 vs. 2.3 0.4 mmol/day, P = 0.002, respectively). Total serum calcium was not different among the three groups; however, serum ionized calcium in women with THP was comparable to that in NT women but significantly higher than that in PE women (1.26 0.01 vs. 1.26 0.01 vs. 1.22 0.01 /mUmol/L, respectively, P = 0.03). PTH levels were similar for THP and NT but were significantly lower than PE (17.4 2.8 vs. 15.4 2.8 vs. 31.7 4.1 ng/L, P = 0.00008). Measurements of 1,25(OH)₂-vitamin D were not significantly different among the three groups (THP: 226 34, NT: 220 13, PE: 162 19 pmol/L; P = 0.19, ANOVA), but direct comparison of NT and PE was still significantly different as reported previously (P = 0.019, t test).

Conclusion: These results provide further evidence that THP and PE may represent distinct and potentially biochemically distinguishable diseases.

Key Words:

• 1,25-Dihydroxyvitamin D
• 25-Hydroxyvitamin D
• Parathyroid hormone
• Preeclampsia
• Pregnancy-induced hypertension