Pregnancy hypertension and preeclampsia

Hypertensive Disorders of Pregnancy & Medical Complications in Pregnancy

Hypertensive disorders complicate up to 10% of all pregnancies in Australia and represent a leading cause of maternal and perinatal morbidity and mortality. Accurate classification, recognition of multi-organ involvement, protocolized management of eclampsia, and rapid differentiation of antepartum haemorrhage are essential core competencies.

Classification of Hypertensive Disorders in Pregnancy

The Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) categorizes hypertensive disorders of pregnancy into four distinct clinical entities:

1. Chronic Hypertension: Hypertension confirmed prior to conception or documented before $20^{+0}$ weeks gestation, or persisting $> 12\text{ weeks}$ postpartum. May be primary (essential, ~90%) or secondary (renal parenchymal disease, renal artery stenosis, endocrine disease).
2. Gestational Hypertension: New-onset hypertension arising at or after $20^{+0}$ weeks gestation with systolic $\text{BP} \ge 140\text{ mmHg}$ and/or diastolic $\text{BP} \ge 90\text{ mmHg}$, in the complete absence of proteinuria or signs of maternal organ dysfunction. Blood pressure typically normalizes within 12 weeks postpartum. Approximately 25% of women with gestational hypertension will subsequently develop pre-eclampsia.
3. Pre-eclampsia: A multi-system endothelial disorder characterized by new-onset hypertension arising at or after $20^{+0}$ weeks gestation accompanied by either proteinuria OR evidence of maternal organ dysfunction:
   • Proteinuria: Documented by a spot urine protein-to-creatinine ratio (PCR) $\ge 30\text{ mg/mmol}$, spot albumin-to-creatinine ratio (ACR) $\ge 8\text{ mg/mmol}$, or 24-hour urine total protein $\ge 300\text{ mg}$.
   • Maternal Organ Dysfunction (diagnostic of pre-eclampsia even in the absence of proteinuria):
     • Renal: Serum creatinine $\ge 90\text{ mcmol/L}$ or doubling of baseline serum creatinine.
     • Maternal haematological dysfunction: Platelets below 150 × 10^9/L can meet the SOMANZ preeclampsia criterion. HELLP commonly uses below 100 alongside haemolysis and liver abnormalities; these are different thresholds.
     • Hepatic: Serum transaminases (ALT or AST) elevated $> 2 \times$ the upper limit of normal, or severe, persistent epigastric or right upper quadrant abdominal pain (reflecting hepatic capsule distension / subcapsular haematoma).
     • Neurological: Severe, intractable frontal/occipital headache, visual disturbances (photopsia, scotomata, diplopia, cortical blindness), hyperreflexia with sustained clonus ($\ge 3\text{ beats}$), or altered mental status.
     • Cardiorespiratory: Acute pulmonary oedema.
     • Fetal-Placental: Fetal growth restriction (estimated fetal weight $< 10\text{th}$ percentile), abnormal umbilical artery Doppler velocimetry (absent or reversed end-diastolic velocity), or oligohydramnios.
4. Pre-eclampsia Superimposed on Chronic Hypertension: Development of new-onset proteinuria, sudden acceleration of blood pressure, or maternal organ dysfunction after 20 weeks gestation in a woman with pre-existing chronic hypertension.

Prevention in High-Risk Women

Women identified at high risk for pre-eclampsia (previous pre-eclampsia, chronic hypertension, pre-existing type 1 or 2 diabetes, chronic kidney disease, antiphospholipid syndrome, or multiple gestation) should be prescribed low-dose aspirin ($100\text{ to }150\text{ mg}$ nocte) commencing between 12 and 16 weeks gestation and continued until 36 weeks. Aspirin selectively inhibits platelet thromboxane A2 production, promoting uteroplacental vascular remodeling.

Antihypertensive Management

Antihypertensive therapy is indicated to reduce maternal cerebrovascular haemorrhage and cardiovascular events. The Australian target blood pressure is systolic $110\text{–}135\text{ mmHg}$ and diastolic $70\text{–}85\text{ mmHg}$:

• First-Line Oral Agents:
  • Labetalol: Combined alpha- and beta-blocker ($100\text{–}400\text{ mg}$ bd/tds). First-line in Australia. Avoid in women with severe asthma.
  • Nifedipine (Sustained-Release): Dihydropyridine calcium channel blocker ($20\text{–}60\text{ mg}$ daily or bd). Safe and effective; avoid sublingual immediate-release capsules due to risk of sudden, uncontrolled hypotension.
  • Methyldopa: Centrally acting alpha-2 agonist ($250\text{–}750\text{ mg}$ tds). Long safety record, but slow onset and carries risks of sedation, depression, and postpartum mood disturbance.
• Severe hypertension in pregnancy: Systolic pressure at least 160 OR diastolic at least 110 mmHg requires urgent confirmation, treatment and obstetric review. Do not require both values to be elevated. Watch for headache, visual disturbance, epigastric pain and organ dysfunction.
  • Intravenous Labetalol: $20\text{–}50\text{ mg}$ IV bolus over 2 minutes, repeatable at 10- to 15-minute intervals up to a maximum cumulative dose of $200\text{ mg}$, or maintenance IV infusion ($20\text{–}160\text{ mg/hour}$).
  • Oral Immediate-Release Nifedipine: $10\text{ mg}$ tablet swallowed (not bitten or chewed), repeatable after 30 minutes if needed.
  • Intravenous Hydralazine: $5\text{–}10\text{ mg}$ slow IV bolus over 20 minutes, repeatable every 20 minutes up to $20\text{ mg}$, followed by infusion ($1.5\text{–}5\text{ mg/hour}$). Frequently causes reflex maternal tachycardia and headache.
• Strictly Contraindicated Antihypertensives: Angiotensin-Converting Enzyme (ACE) inhibitors, Angiotensin II Receptor Blockers (ARBs), and direct renin inhibitors are strictly contraindicated throughout pregnancy due to severe fetotoxicity (oligohydramnios, renal dysgenesis, pulmonary hypoplasia, neonatal renal failure, and calvarial hypoplasia).

Delivery Timing in Pre-eclampsia

Delivery is the only definitive curative therapy for pre-eclampsia:

• Gestational age $\ge 37^{+0}$ weeks: Planned delivery is indicated regardless of severity.
• Gestational age $< 34^{+0}$ weeks: Expectant management under strict maternal-fetal inpatient surveillance is attempted if both mother and fetus remain stable. Betamethasone (11.4 mg IM, two doses 24 hours apart) is administered to accelerate fetal surfactant production. Indications for immediate delivery at any gestational age include uncontrollable severe hypertension, eclampsia, pulmonary oedema, platelet count $< 50 \times 10^9\text{/L}$, deteriorating renal/liver function, placental abruption, or non-reassuring fetal status.

Primary references (checked 7 October 2026): Queensland maternity guidelines.