Gestational hypertension and preeclampsia are two illnesses that are feared by pregnant women. Preeclampsia is a rapidly progressive condition characterized by high blood pressure and damage to the expectant mother's kidneys. Untreated, they can lead to life-threatening medical problems for the mother and complications for the baby, including low birth weight and size, respiratory distress, long-term neurological problems and even death.

But the good news is that both may be preventable simply by increasing an expectant mother's daily calcium intake, according to a new systematic review.

"Pregnant women from communities with low dietary calcium who took at least 1.5 grams of calcium as a supplement during the second half of pregnancy had a lower risk of hypertension and preeclampsia, and of severe complications including death, than women who received placebo treatment," said lead review author Dr. G.J. Hofmeyr, head of the obstetrics and gynecology department, East London Hospital Complex in South Africa. 1.5 grams is several times more than the amount of calcium found in most multivitamins.

The results were similar, but less dramatic, for women with better prenatal nutrition: "Women from communities with adequate dietary calcium had a small (10 percent) reduction in the risk of hypertension, but no significant reduction in the risk of preeclampsia or other adverse outcomes," said Hofmeyr. The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research.

The authors looked at 12 studies, one involving more than 4,000 women in North America. The most recent of the studies — conducted by the World Health Organization — involved more than 8,000 pregnant women internationally.

High blood pressure is the primary cause of premature birth and is the leading cause of newborn deaths, particularly in low-income countries. A new report from the Institute of Medicine found that 12.5 percent of U.S. births are premature and cost society an estimated $26 billion a year.

The Cochrane review found that calcium supplementation during pregnancy is a safe and relatively inexpensive way to reduce the risk of high blood pressure. "Calcium supplementation may be of some benefit in reducing the morbidity associated with preeclampsia, and it does no harm," said Dr. John T. Repke, chairman of obstetrics and gynecology at Penn State University College of Medicine.

Hypertensive disease occurs in approximately 12 percent to 22 percent of pregnancies and is directly responsible for 17.6 percent of maternal deaths in the United States alone, according to the American College of Obstetrics and Gynecology.

Preeclampsia affects an estimated 5 percent to 6 percent of first-time moms. The exact cause is unknown and the only cure is delivery.