It's long been known that chocolate can contribute to a healthy heart and reduce hypertension because it contains a chemical called theobromine, a natural blood vessel dialator and muscle relaxer.

Preeclampsia occurs when a pregnant mother's blood pressure skyrockets and protein spills into the urine. The condition shares many of the same characteristics as heart disease and hypertension. It affects 3 percent to 8 percent of pregnancies.

A Yale research study published in the May issue of Epidemiology tracked chocolate consumption in more than 2,000 woman during their first and third trimesters and later analyzed umbilical cord blood to determine the levels of theobromine.

Woman who ate the most chocolate as measured by cord blood concentrations (about 5 or more servings per week) had a lower risk of preeclampsia, the study found. Woman who had the highest theobromine levels were 69 percent less likely to develop the condition than those who consumed the least, according to the report.

Study author Elizabeth W. Triche hypothesized that theobromine may improve circulation in the placenta and reduce damage caused by having low antioxidant levels.