Extract: During pregnancy calcium requirements increase principally as a result of high calcium accretion in the fetus (30 gm). To afford this requirement intestinal absorption of calcium increases, while renal resorption decreases as calcium in maternal bone tends to be preserved. Therefore a slight decline in serum ionic calcium and a rise in parathyroid hormone (PTH) levels are seen. The increase of PTH levels during pregnancy may depend on calcium intake. Several studies have shown an inverse relationship between calcium intake and blood pressure in pregnant and nonpregnant animals as well as in humans. Also, calcium intake seems to be lower in hypertensive pregnant and nonpregnant subjects. The mechanism of this association is not fully understood. It is hypothesized that a rise in PTH could be associated with an increase in free calcium in cell cytosol. This Ca++ intracellular increase can be related to hypertonicity of muscular arteriolar cells.(author)