Calciotropic hormones during reproduction.

This review summarizes the reported effects of the menstrual cycle, pregnancy and lactation on serum concentration of the calciotropic hormones PTH and 1,25(OH)2D. A midcycle rise in PTH and 1,25(OH)2D has been observed, but in the majority of studies there was no change in PTH and 1,25(OH)2D concentrations throughout the menstrual cycle. Both total and free 1,25(OH)2D levels are increased during pregnancy. The renal 1,25(OH)2D production is stimulated, and there is some evidence of 1,25(OH)2D production by decidua/placenta and fetal kidney in vitro; the decidual/placental production should not be overestimated in vivo. The increased renal 1 alpha-hydroxylase activity is possibly mediated by estrogens and PTH, although the effect of pregnancy on PTH remains uncertain. Increased serum 1,25(OH)2D concentrations probably result in a rise of intestinal calcium absorption during pregnancy. There is a postdelivery drop in PTH and 1,25(OH)2D levels, but they are increased when lactation is prolonged, or in mothers nursing twins. The l alpha-hydroxylase activity during lactation may be stimulated by PTH, but also by prolactin.