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 (E(2)), prolactin and 1,25-dihydroxyvitamin D (1,25(OH)(2)D) 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, E(2) was low (p < 0.05); prolactin decreased according to lactation status (p < 0.05). 1,25(OH)(2)D 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)(2)D 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 E(2) levels and perhaps increased parathyroid hormone-related protein levels.
Osteoporosis International, 2012, Vol 24, Issue 4, p. 1307-1320