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Changes in calcitropic hormones, bone markers and insulin-like growth factor I (IGF-I) during pregnancy and
U K Møller1, S Streym, L Mosekilde
1Department of Endocrinology and Internal Medicine, Aarhus University Hospital, and Department of Clinical Medicine, Faculty of Health Sciences, Aarhus University, Tage Hansens Gade 2, 8000, Aarhus C, Denmark. kristine.moller@ki.au.dk
Unlabelled:
Pregnancy and lactation cause major changes in calcium homeostasis and bone metabolism. This population-based cohort study presents the physiological changes in biochemical indices of calcium homeostasis and bone metabolism during pregnancy and lactation
Introduction:
We describe physiological changes in calcium homeostasis, calcitropic hormones and bone metabolism during pregnancy and lactation.
Methods:
We studied 153 women planning pregnancy (n=92 conceived) and 52 non-pregnant, age-matched female controls. Samples were collected prior to pregnancy, once each trimester and 2, 16 and 36 weeks postpartum. The controls were followed in parallel.
Results:
P-estradiol (E2), prolactin and 1,25-dihydroxyvitamin D (1,25(OH)2D) increased (p<0.001) during pregnancy, whereas plasma levels of parathyroid hormone (P-PTH) and calcitonin decreased (p<0.01). Insulin-like growth factor I (IGF-I) was suppressed (p<0.05) in early pregnancy but peaked in the third trimester. Postpartum, E2 was low (p<0.05); prolactin decreased according to lactation status (p<0.05). 1,25(OH)2D was normal and IGF-I was again reduced (p<0.05). P-PTH and calcitonin increased postpartum. From early pregnancy, markers of bone resorption and formation rose and fall, respectively (p<0.001). From the third trimester, bone formation markers increased in association with IGF-I changes (p<0.01). Postpartum increases in bone turnover markers were associated with lactation status (p<0.001). During lactation, plasma phosphate was increased, whereas calcium levels tended to be decreased which may stimulate PTH levels during and after prolonged lactation.
Conclusion:
The increased calcium requirements in early pregnancy are not completely offset by increased intestinal calcium absorption caused by high 1,25(OH)2D since changes in bone markers indicated a negative bone balance. The rise in bone formation in late pregnancy may be initiated by a spike in IGF-I levels. The high bone turnover in lactating women may be related to high prolactin and PTH levels, low E2 levels and perhaps increased parathyroid hormone-related protein levels.
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