Pregnant women occasionally experience an increase in blood pressure known as gestational hypertension or pregnancy-induced hypertension (PIH). In a more severe condition called pre-eclampsia, a rise in blood pressure is accompanied by protein in the urine and sometimes by sudden weight gain, swelling in the face or hands, and other symptoms. When left untreated, pre-eclampsia can lead to seizures (called eclampsia) or liver, kidney, or bleeding problems in the mother and distress or delayed growth in the fetus. Unless pre-eclampsia is mild, doctors usually seek to deliver the baby early.

Although there are no fully established natural treatments for the prevention of pre-eclampsia or PIH, calcium has shown significant promise.

Calcium

A meta-analysis (statistical review) of 11 studies of calcium supplementation in pregnancy, involving a total of more than 6,000 women, found that calcium slightly reduced the risk of pre-eclampsia and hypertension, particularly in two groups of women: those at high risk for hypertension and/or those with low calcium intakes.1

However, by far the largest single study in the meta-analysis found no benefits.2 In this double-blind study, researchers gave either 2 g of calcium or placebo daily to 4,589 women from weeks 13 to 21 of their pregnancy onward. In the end, researchers found no significant decreases in rates of hypertension or pre-eclampsia—not even when they looked specifically at women whose daily calcium consumption mirrored that of women in developing countries.

The meta-analysis included this negative study in its calculations, but still found that calcium seemed to be helpful.

In a subsequent double-blind, placebo-controlled study published in 2006 and conducted by the World Health Organization, calcium supplements (1.5 g per day) were tried in 8,325 pregnant women whose calcium intake was inadequate.28 Calcium failed to reduce the incidence of pre-eclampsia. However, it did appear to reduce the severity of pre-eclampsia episodes.

The bottom line: Calcium might be of some benefit for those pregnant women who are at high risk for hypertension or deficient in calcium. However, for well-nourished, low-risk women, effects are likely to be minimal or nil.

All of the above refers to preventing pre-eclampsia. One double-blind, placebo-controlled study suggests that calcium supplements are noteffective for treating pre-eclampsia that has already developed.3

Note:Calcium appears to offer the additional benefit of reducing blood levels of lead during pregnancy.4

Interestingly, weak evidence hints that use of calcium by pregnant mothers might reduce risk of hypertension in their children.33

For more information, including dosage and safety issues, see the full Calcium article.