Medical Definition of ECLAMPSIA. : a convulsive state: an attack of convulsions: as a: convulsions or coma late in pregnancy in an individual affected with preeclampsia—compare toxemia of pregnancy b: a condition comparable to milk fever of cows occurring in domestic animals (as dogs and cats).edical Definition of ECLAMPSIA. : a convulsive state: an attack of convulsions: as a: convulsions or coma late in pregnancy in an individual affected with preeclampsia—compare toxemia of pregnancy b: a condition comparable to milk fever of cows occurring in domestic animals (as dogs and cats).