Affecting at least 5 percent to 8 percent of all pregnancies, pre-eclampsia is a rapidly progressive condition characterized by high blood pressure, the presence of protein in the urine, swelling, sudden weight gain and headaches, although some women report few symptoms. Women who have previously given birth to a child have lower risk of pre-eclampsia, the researchers said.

The study, published in the International Journal of Epidemiology, shows that women who have had two or more induced abortions reduced their risk for pre-eclampsia by 60 percent. Women who have had one abortion have an approximately 16 percent reduced risk for pre-eclampsia compared with women who have never had an abortion.

The researchers said the results indicate that every normal pregnancy, even if it ends before birth, to some degree will protect against pre-eclampsia in a later pregnancy, almost like a vaccination.