Pre-eclampsia is a condition that causes pregnant women to retain water and swell at their ankles, hands, feet and face. Other symptoms include high blood pressure, headaches and light sensitivity. If left untreated, pre-eclampsia may result in vomiting, convulsions and kidney, liver or brain damage. Severe cases may result in death. Pre-eclampsia is usually detected during prenatal visits, and controlled through diet and medications.

In a recent international study, magnesium supplementation reduced the risk of pre-eclampsia in pregnant women by more than half. Women in 33 countries were given either magnesium sulphate or a placebo in a double-blind fashion. At trial end, researchers determined that women given the magnesium had a 58% lower risk of pre-eclampsia. The risk of placental abruption and maternal mortality was also lower among women given magnesium. Though women did report some side effects from magnesium, the researchers say they did not appear to be harmful to mother or baby.

In a related study from Beijing Medical University, 51 pregnant women were given a low dose of magnesium gluconate (3 g per day) while 51 other pregnant women were given a placebo. This trial started during the 28th week of pregnancy and lasted until delivery. The goal of the trial was to see if magnesium could prevent pregnancy-induced hypertension or high blood pressure. The end results showed that 16% of women in the placebo group developed hypertension, while only 4% of women taking magnesium developed the complication.

Sources: Lancet 2002 Jun 1;359(9321):1877-90; Zhonghua Fu Chan Ke Za Zhi 1997 Oct;32(10):613-15