Msm. Ardawi et al., CALCIUM-REGULATING HORMONES AND PARATHYROID HORMONE-RELATED PEPTIDE IN NORMAL HUMAN-PREGNANCY AND POSTPARTUM - A LONGITUDINAL-STUDY, European journal of endocrinology, 137(4), 1997, pp. 402-409
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.