Abnormal 1,25-dihydroxyvitamin D metabolism in preeclampsia.

We previously reported that preeclampsia is associated with hypocalciuria (N Engl J Med 1987; 316:715). The purpose of this study was to determine whether alterations in calcium regulatory hormones are present in preeclampsia and, if so, whether they are responsible for hypocalciuria. Thirty-two pregnant women were studied in the second and third trimesters of pregnancy (11 women with preeclampsia, nine with chronic hypertension, and 12 normotensive women). 1,25-Dihydroxyvitamin D, C-terminal parathyroid hormone, ionized calcium, and urinary calcium excretion were measured. 1,25-Dihydroxyvitamin D was significantly lower in the women with preeclampsia in the third trimester when the disease developed (37.8 +/- 15 pg/ml) than in women with chronic hypertension (75 +/- 15 pg/ml, p less than 0.05) and normal women (65 +/- 10 pg/ml, p less than 0.05). Parathyroid hormone was higher, but not significantly, in those with preeclampsia. Ionized calcium was not significantly different among the three groups. Urinary calcium excretion was abnormally low for pregnancy (less than 50 mg/24 hr) in all but one women with preeclampsia. We conclude that 1,25-dihydroxyvitamin D is reduced in preeclampsia and may lead to hypocalciuria by causing decreased intestinal absorption of calcium, stimulation of parathyroid hormone, and increased distal renal tubular resorption of calcium. The cause of reduced 1,25-dihydroxyvitamin D in preeclampsia is unknown and may be due to either diminished renal or placental production of the hormone.