A PROSPECTIVE-STUDY OF CALCIOTROPIC HORMONES IN PREGNANCY AND POST-PARTUM - RECIPROCAL CHANGES IN SERUM INTACT PARATHYROID-HORMONE AND 1,25-DIHYDROXYVITAMIN-D

OBJECTIVE: The purpose of this study was to examine the hormones regul ating calcium homeostasis longitudinally in pregnancy and post parium. STUDY DESIGN: Twenty-three women with normal pregnancies were studied in the second and third trimesters and post partum. At each time bloo d was analysed for ionized calcium, vitamin D metabolites, and intact parathyroid hormone, and a 24-hour urine specimen was analysed for cre atinine, calcium, and sodium. RESULTS: Urinary calcium excretion was 2 50% to 300% higher during pregnancy than post partum (P < 0.00001). 1, 25-Dihydroxyvitamin D levels were equivalent in the second and third t rimesters but were twofold higher than postpartum values (p < 0.01). I onized calcium was similar at all time points. Intact parathyroid horm one in the second and third trimesters was 50% of postpartum levels (p < 0.001). CONCLUSION: Pregnancy is associated with an increase in the levels of 1,25-dihydroxyvitamin D and a concomitant reciprocal fall i n intact parathyroid hormone levels. The increase in serum 1,25-dihydr oxyvitamin D values appears to be a key factor in providing for the in crease in maternal calcium requirements during pregnancy.