CALCIUM-REGULATING HORMONES AND PARATHYROID HORMONE-RELATED PEPTIDE IN NORMAL HUMAN-PREGNANCY AND POSTPARTUM - A LONGITUDINAL-STUDY

Objectives: To evaluate calcium-regulating hormones and parathyroid ho rmone-related peptide (PTHrP) in normal human pregnancy and postpartum in women not deficient in vitamin D. Design: A prospective longitudin al study was conducted in pregnant Saudi women during the course of pr egnancy (n = 40), at term and 6 weeks postpartum (n = 18). Maternal co ncentrations of serum calcidiol and calcitriol were determined, togeth er with those of serum intact-parathyroid hormone (PTH), PTHrP, calcit onin, osteocalcin, human placental lactogen (hPL), prolactin, vitamin D binding protein, alkaline phosphatase, calcium, phosphate and magnes ium. A group of non-pregnant women (n = 280) were included for compara tive purposes. Results: The calcidiol concentrations decreased (mean+/ -S.D.) significantly from 54+/-10 nmol/l in the first trimester to 33/-8 nmol/l in the third trimester (P < 0.001) and remained decreased a t term and postpartum (both P < 0.001). The calcitriol concentration i ncreased through pregnancy, from 69+/-17 pmol/l in the first trimester to 333+/-83 pmol/l at term (P < 0.001). Intact-PTH concentrations inc reased from 1.31+/-0.25 pmol/l in the first trimester to 2.26+/-0.39 p mol/l in the second trimester, but then declined to values of the firs t trimester and increased significantly postpartum (4.02+/-0.36 pmol/l ) (P < 0.001). PTHrP concentration increased through pregnancy from 0. 81+/-0.12 pmol/l in the first trimester to 2.01+/-0.22 pmol/l at term and continued its increase postpartum (2.63+/-0.15 pmol/l) (P < 0.001) . Significant positive correlations were evident between PTHrP and alk aline phosphatase up to term (r = 0.051, P < 0.001) and between PTHrP and calcitriol (r = 0.46, P < 0.001), osteocalcin (r = 0.23, P < 0.05) and prolactin (r = 0.41, P < 0.05) during pregnancy. Osteocalcin star ted to increase from 0.13+/-0.01 nmol/l in the second trimester, throu gh pregnancy and postpartum (P < 0.001). Calcitonin was increased more than twofold by the second trimester compared with the first trimeste r (P < 0.001) and subsequently decreased (P < 0.001). Prolactin concen trations were significantly greater in the second (6724+/-1459 pmol/l) and third (8394+/-2086 pmol/l) trimesters compared with values before pregnancy (P < 0.001). hPL increased throughout the course of pregnan cy, reaching a maximum at term (7.61+/-2.57 mu IU/ml). There was no di rect correlation between serum calcitriol concentrations during pregna ncy and serum prolactin (r = -0.12, P < 0.19) or serum hPL (r = 0.17, P < 0.21). Significant changes were observed in the serum concentratio ns of calcium and phosphate, but not in that of magnesium, during the course of pregnancy; calcium concentrations showed a maximal decrease at term. Conclusions: Changes in serum PTHrP during the course of preg nancy, at term and postpartum have been demonstrated, suggesting that the placenta (during pregnancy) and mammary glands (postpartum) are th e main sources of PTHrP. No support for the concept of 'physiological hyperparathyroidism' of pregnancy could be demonstrated in the present work. The pregnancy-induced increase in calcitriol concentration may thus be the primary mediator of the changes in maternal calcium metabo lism, but the involvement of other factors cannot be excluded.