Calcium, vitamin D and parathyroid hormone relationships in pregnant Caucasian and Asian women and their neonates

Plasma calcium, serum 25 hydroxyvitamin D [25(OH)D], 1,25 dihydroxyvitamin D[1,25(OH)₂D] and parathyroid hormone (PTH) have been measured in pregnant and newborn Caucasians and Asians. Calcium and 25(OH)D concentrations were lower in Caucasian than in Asian women at all four stages (thee trimesters and during labour) of pregnancy. PTH concentrations were greater in Asian than in Caucasian women during the three trimesters, but not at labour, and increased in both groups through pregnancy, without a concomitant change in plasma calcium concentrations. There was a significant inverse correlation between calcium and PTH, as well as 25(OH)D and PTH, concentrations. These data demonstrate the presence of progressive 'hyperparathyroidism' during pregnancy in Caucasian and Asian women. The higher PTH concentrations in Asian women may reflect the necessity of maintaining adequate plasma calcium concentrations through PTH-induced osteolysis in the face of vitamin D deficiency. Relative hyperparathyroidism in Asians may contribute to net loss of calcium from the skeleton and osteopenia in Asian women. Calcium, 25(OH)D and 1,25(OH)₂D concentrations were lower, and those of PTH higher, in Asian newborns compared with Caucasian newborns. Serum 1,25(OH)₂D concentrations in the Asian newborn, though lower than respective maternal levels, were comparable with normal adult levels, indicating that 1,25(OH)₂D biosynthesis is stimulated in the Asian newborn to compensate for the low serum 25(OH)D concentrations.