Clinical overview
The hypertensive disorders of pregnancy are, alongside obstetric haemorrhage and non-pregnancy-related infection, one of the leading direct causes of maternal death in South Africa, recurring triennium after triennium in the Saving Mothers (NCCEMD) reports. The tragedy of the SA picture is that most hypertensive deaths are judged avoidable — the recurring lessons are failure to measure blood pressure properly, failure to recognise severity, delay in giving magnesium sulphate and antihypertensives, delay in delivery, and inappropriate transfer of unstable women. A registrar must therefore treat hypertension in pregnancy not as a benign antenatal label but as a condition that kills mothers and babies through stroke, eclampsia, pulmonary oedema, abruption, HELLP, acute kidney injury and iatrogenic prematurity.
This chapter covers the classification and management of all forms of pregnancy hypertension — chronic hypertension, gestational (pregnancy-induced) hypertension, pre-eclampsia, and chronic hypertension with superimposed pre-eclampsia — and the drills for the two emergencies they generate: severe hypertension and eclampsia. The pathophysiology and detailed management of pre-eclampsia and HELLP are developed further in Pre eclampsia and HELLP; the fetal growth restriction that frequently accompanies placental hypertensive disease is covered in Intrauterine growth restriction; and resuscitation of the collapsed or convulsing mother in Resuscitation in pregnancy.
Core knowledge
Definitions and classification
Hypertension in pregnancy is defined as a systolic blood pressure ≥140 mmHg and/or diastolic ≥90 mmHg, confirmed on repeat measurement, using a correctly sized cuff with the woman seated and the arm supported at heart level. The standard classification (aligned across NICE NG133 and the SA Maternity Guideline) is:
- Chronic hypertension — present before pregnancy or before 20 weeks' gestation, or persisting beyond 6 weeks postpartum. May be essential or secondary (renal, endocrine, coarctation).
- Gestational hypertension — new hypertension arising after 20 weeks without proteinuria or other features of pre-eclampsia. A proportion progress to pre-eclampsia, so it is not a benign endpoint.
- Pre-eclampsia — new hypertension after 20 weeks with proteinuria or other maternal organ dysfunction (renal, hepatic, neurological, haematological) or uteroplacental dysfunction (fetal growth restriction). Note the contemporary definition no longer requires proteinuria if other organ involvement is present.
- Chronic hypertension with superimposed pre-eclampsia — the highest-risk group; suspected when a woman with chronic hypertension develops new/worsening proteinuria, a sudden rise in BP needing escalation of treatment, or new organ dysfunction.
Severe hypertension is a sustained systolic ≥160 mmHg and/or diastolic ≥110 mmHg — the threshold above which the risk of maternal stroke rises sharply and which mandates urgent treatment regardless of the underlying category. This is the single most important number on the page.
Figure J19.1 — Classification, severe BP threshold and major complications of hypertension in pregnancy.
Pathophysiology in brief
Pre-eclampsia is a disorder of abnormal placentation: failure of trophoblast to fully remodel the spiral arteries leaves them high-resistance, producing placental ischaemia and the release of anti-angiogenic factors (notably soluble fms-like tyrosine kinase-1, sFlt-1) that antagonise placental growth factor (PlGF) and vascular endothelial growth factor. The result is a systemic maternal endothelial dysfunction causing vasoconstriction (hypertension), increased capillary permeability (oedema, proteinuria, pulmonary oedema), a procoagulant state and end-organ ischaemia. This explains why the only definitive cure is delivery of the placenta, and why disease can still worsen for 24–48 hours postpartum. The mechanistic detail is expanded in Pre eclampsia and HELLP.
Figure J19.2 — Placenta-driven endothelial dysfunction explains the multisystem complications of pre-eclampsia.