What are the signs of preeclampsia and when does it become an emergency?

Preeclampsia is a hypertensive disorder of pregnancy occurring after 20 weeks gestation, characterized by blood pressure of 140 over 90 or higher on two occasions and proteinuria or end-organ dysfunction. Warning signs include sudden weight gain, facial and hand edema, headache that does not respond to treatment, visual disturbances like seeing spots, and right upper quadrant or epigastric pain indicating liver involvement.