Hypertensive disorders are the most common medical complications of pregnancy. Hypertensive disorders are associated with increased maternal and perinatal mortality and present as a wide spectrum of disorders, ranging from minimal elevation of blood pressure alone to severe hypertension with multiple organ dysfunction. Gestational hypertension may be defined as elevated blood pressure appearing after the 20th week of pregnancy or in the first 24 hours postpartum without edema or proteinuria, and with a return to normotension within 10 days of delivery. The classifications and definitions of the hypertension disorders of pregnancy are frequently confusing. It is often difficult to differentiate between pre-eclampsia, chronic hypertension, and chronic hypertension with superimposed pre-eclampsia. Pre-eclampsia is a disorder specific to human pregnancy. Pre-eclampsia may be classified as either mild or severe. The endothelium and the internal elastic lamina are replaced by invading trophoblast tissue.