Eclampsia (Greek, "shining forth"), an acute and life-threatening complication of pregnancy, is characterized by the appearance of tonic-clonic seizures, usually in a patient who had developed pre-eclampsia. (Preeclampsia and eclampsia are collectively called Hypertensive disorder of pregnancy and toxemia of pregnancy.)

Eclampsia includes seizures and coma that happen during pregnancy but are not due to preexisting or organic brain disorders.

Typically patients show signs of pregnancy-induced hypertension and proteinuria prior to the onset of the hallmark of eclampsia, the eclamptic convulsion. Other cerebral signs may precede the convulsion such as nausea, vomiting, headaches, and cortical blindness. In addition, with the advancement of the pathophysiological process, other organ symptoms may be present including abdominal pain, liver failure, signs of the HELLP syndrome, pulmonary oedema, and oliguria. The foetus may already have been compromised by intrauterine growth retardation, and with the toxemic changes during eclampsia may suffer foetal distress. Placental bleeding and placental abruption may occur.