Past names: pregnancy induced hypertension, pre-eclamptic toxaemia (both outdated) (1).
Definition:

• Pre-eclampsia: hypertension arising after 20 weeks' gestation, with one or more organ system involvement. There is resolution of the disease by three months postpartum (1,2).
• Severe pre-eclampsia: blood pressure systolic >=160 mmHg and/or diastolic >=110 mmHg and extreme derangements of organ function (1).
  

Variants:

• HELLP syndrome (haemolysis, elevated liver enzymes, low platelets) (1).
• Under extremely rare circumstances, pre-eclampsia may develop before 20 weeks' gestation in the setting of a hydatiform mole, multiple pregnancy, fetal or placental abnormalities, antiphospholipid syndrome or severe renal disease (1).
  

Differential diagnosis:

• Acute fatty liver of pregnancy: rare condition of pregnancy, which is not associated with hypertension (1).
• Haemolytic uraemic syndrome (HUS)/thrombotic thrombocytopenic purpura (TTP): thrombocytopenia, microangiopathic hyemolytic anemia, neurological symptoms and signs, renal function abnormalities, fever (1).
• Renal disease (1).
• Phaechromocytoma (1).
• Drug usage: cocaine, amphetamines (1).
• Cardiovascular diseases: coarctation, subclavian stenosis, aortic dissection, vasculitis (1).
  

Prevalence: the disease is complicating 5-8% of pregnancies(1). In the UK 27.5 cases/100'000 maternities (2006-2008) (3).
Morbidity: severe maternal complications include antepartum hemorrhage due to placental abruption, eclampsia, cerebrovascular accidents, organ failure and disseminated intravascular coagulation. Pre-eclampsia is the leading cause of fetal growth restriction and preterm birth (1,2).
Mortality: deaths are due to intracranial haemorrhage and cerebral infarction, acute pulmonary oedema, respiratory failure and hepatic failure or rupture. Pre-eclampsia is the leading cause of intrauterine fetal demise (1,2). In the UK: 0.83 death/100'000 maternities (2006-2008) (3).
Measurements:

• Blood pressure should be measured at rest, using korotkoff V as the diastolic value, with an appropriately sized blood pressure cuff. Initial blood pressure should be measured with a calibrated manual auscultatory device, as automatic systems often underestimate systolic blood pressure (1,4). Repeated measurements of blood pressure confirming sustained hypertension should be made and these are usually done at four-hourly intervals (1).
• During labor, blood pressure measurement should be hourly in women with mild or moderate hypertension, or continually monitored in women with severe hypertension (5).
  

Treatment: delivery of the baby and removing the placenta is currently the only definitive way of curing the condition (1). For aspects specific to anaesthesiology see the corresponding article in the "periop" section.
Future risks: women who experience pre-eclampsia are at increased risk of hypertension, cerebrovascular disease an ischemic heart disease, in later life (1).

References:

1. Management of pre-eclampsia. Anaesthesia 2012,67,1009-1020: full text | pdf
2. Blaubuch Frauenklinik KSA: link (Nr. 59/2)
3. Saving Mothers’ Lives: Reviewing maternal deaths to make motherhood safer: 2006–2008. BJOG: An International Journal of Obstetrics & Gynaecology,2011,118:1–203. doi:10.1111/j.1471-0528.2010.02847.x: pdf
4. AHA Scientific Statement: Recommendations for Blood Pressure Measurement in Humans and Experimental Animals. Hypertension 2005;45:142-161: full text | pdf
5. The management of hypertensive disorders during pregnancy. National Institute for Health and Clinical Excellence Guideline (revised reprint January 2011): link.