However, more recent research indicates that the previously reported hyperparathyroidism of pregnancy may be an artifact of earlier radioimmunoassay methods. Serum ionic calcium changes are minimal (Pitkin et al., 1979).Įarly studies indicated that the level of parathyroid hormone (PTH) increases progressively in late pregnancy, it was reported to be approximately 50% higher than prepregnancy levels (Pitkin et al., 1979). When adjustments are made for changes in serum albumin or protein concentration, little or no change in the total serum calcium level is apparent during pregnancy.
This is associated with and parallels the drop in serum albumin (to which 60% of the serum calcium is attached) that results from expansion of the extracellular fluid volume. Total serum calcium decreases gradually throughout pregnancy. These include changes in calcium-regulating hormones, which affect intestinal absorption, renal reabsorption, and bone turnover of calcium. Several changes in calcium metabolism associated with pregnancy facilitate the transfer of calcium from mother to fetus while protecting calcium levels in maternal serum and bone.
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