Calcium supplementation has been shown to reduce hypertension in pregnancy. However the reduction in the risk for preeclampsia from calcium supplementation is small.

Other measures once used are no longer favored:

Dietary sodium restriction and diuretics reduce blood volume without a significant effect upon blood pressure. Aspirin--previously thought to reduce the risk for preeclampsia. However this is not supported by two large, multicenter, rando mized trials.

{Ref Sibai BM. Treatment of hypertension in pregnant women. N Engl J Med 1996; 335:257-266.}