Hypertensive Disorders of Pregnancy

Hypertensive disorders of pregnancy are a spectrum of conditions defined by raised blood pressure in the pregnant state, ranging from gestational hypertension through pre-eclampsia, with its multisystem involvement, to eclampsia. They are among the leading causes of maternal and perinatal morbidity and death worldwide.

Definition

Hypertensive disorders of pregnancy comprise chronic hypertension, gestational hypertension (new hypertension after 20 weeks without features of pre-eclampsia), pre-eclampsia (new hypertension with proteinuria or other maternal organ dysfunction), and eclampsia (pre-eclampsia complicated by seizures).

Scope

This entry covers the classification of the hypertensive disorders of pregnancy, the placental and endothelial mechanisms underlying pre-eclampsia, the principal maternal and fetal consequences, and the structure of evidence and guidelines. It treats the topic as a clinical entity for reference and does not provide dosing or individualised management.

Core questions

• How are the hypertensive disorders of pregnancy classified and distinguished from one another?
• What placental and vascular mechanisms are thought to drive pre-eclampsia?
• Which maternal and fetal complications define the severity of these disorders?
• How has the diagnostic definition of pre-eclampsia evolved, particularly regarding proteinuria?

Key concepts

• Gestational hypertension
• Pre-eclampsia and severe features
• Eclampsia
• Proteinuria and maternal organ dysfunction
• Spiral-artery remodelling and placentation
• Endothelial dysfunction
• Angiogenic and anti-angiogenic factors

Key theories

Two-stage (placental) model of pre-eclampsia

Proposes that deficient remodelling of the spiral arteries and impaired placentation (stage one) lead to placental ischaemia and release of circulating factors that cause widespread maternal endothelial dysfunction and the clinical syndrome (stage two), linking the placental origin to the multisystem maternal presentation.

Mechanisms

Pre-eclampsia is widely modelled as a disorder originating in the placenta. In early pregnancy, inadequate trophoblast invasion and incomplete remodelling of the uterine spiral arteries are thought to produce a poorly perfused, ischaemic placenta. The ischaemic placenta is proposed to release imbalanced angiogenic and anti-angiogenic factors and other mediators into the maternal circulation, causing generalised endothelial dysfunction that manifests as hypertension, increased vascular permeability and proteinuria, and dysfunction of the liver, kidney, brain, and coagulation system (Sibai and colleagues, 2005; Mol and colleagues, 2016). Gestational hypertension lacks these multisystem features, and eclampsia represents progression to seizures.

Clinical relevance

These disorders are a major cause of maternal death, severe maternal morbidity, iatrogenic preterm birth, and fetal growth restriction, and they are central to antenatal surveillance. This entry describes the classification, mechanisms, and consequences as a reference framework; it is not a source of dosing or individualised treatment recommendations.

Epidemiology

Hypertensive disorders complicate a substantial minority of pregnancies and rank among the leading direct causes of maternal mortality globally, with disproportionate impact in lower-resource settings (Sibai and colleagues, 2005; Mol and colleagues, 2016).

Evidence & guidelines

Classification and diagnostic criteria are set out in professional guidelines, which revised the definition of pre-eclampsia so that proteinuria is no longer mandatory when other features of maternal organ dysfunction are present (American College of Obstetricians and Gynecologists Task Force, 2013; American College of Obstetricians and Gynecologists, 2020). Narrative reviews summarise the placental-endothelial model and its evidence (Sibai and colleagues, 2005; Mol and colleagues, 2016).

History

Eclamptic seizures have been described since antiquity, and the link to raised blood pressure and proteinuria was established as clinical measurement developed. Twentieth-century work framed pre-eclampsia as a placental disorder, and the two-stage model and the discovery of circulating angiogenic factors refined that account. Diagnostic definitions have since been broadened to recognise pre-eclampsia without proteinuria when other organ dysfunction is present.

Debates

Is proteinuria required to diagnose pre-eclampsia?

Guidelines moved away from requiring proteinuria, allowing diagnosis when new hypertension is accompanied by other maternal organ dysfunction; this broadens the diagnostic category and changes which pregnancies are labelled, a shift that remains the subject of refinement.

Seminal works

• sibai-2005
• mol-2016
• acog-hip-2013

Frequently asked questions

What is the difference between gestational hypertension and pre-eclampsia?

Gestational hypertension is new high blood pressure after 20 weeks without features of organ involvement, whereas pre-eclampsia adds proteinuria or other maternal organ dysfunction, reflecting a systemic disorder rather than isolated hypertension.

Why is pre-eclampsia considered a placental disorder?

Evidence points to abnormal placentation and an ischaemic placenta releasing factors that cause widespread maternal endothelial dysfunction, which is why delivery of the placenta is the definitive resolution of the syndrome.