A complication of pregnancy, affecting about 5% of all women, characterized by hypertension and damage to the linings of the blood vessels of the brain, liver, lungs, and kidneys, which can lead to multiple organ failure, convulsions, coma, and death. The only cure is delivery of the child.
There are no categorical antonyms for preeclampsia. However, one could loosely use, e.g., uncomplicated pregnancy, normal pregnancy, etc., as antonyms.