Pregnancy-induced hypertension and low birth weight: the role of calcium.

Considerable interest has developed regarding the role of calcium in the regulation of blood pressure. Epidemiologic investigations, laboratory evaluations, and clinical trials all confirm that the relationship between calcium and blood pressure extends to include the pregnant state. On the basis of current information it is clear that calcium supplementation during pregnancy lowers blood pressure. Additionally, the effect of calcium on blood pressure may influence the incidence and/or gestational age of development of preeclampsia. Additionally, the effect on smooth-muscle relaxation detected in calcium-supplemented patients may affect the incidence of prematurity. Although the mechanism for these effects has not been entirely elucidated, calcium supplementation appears to affect circulating concentrations of parathyroid hormone and renin, which may modulate intracellular ionized calcium, resulting in the observed effect on smooth-muscle relaxation. This effect may also be responsible for reduced uterine activity and for a lowering of the incidence of prematurity.