What is the definition of gestational hypertension?

Definition of Gestational Hypertension

Gestational hypertension is pregnancy-induced hypertension (blood pressure ≥140/90 mmHg) that develops after 20 weeks of gestation in a previously normotensive woman, without significant proteinuria, and typically resolves within 42 days postpartum. 1

Key Diagnostic Criteria

Blood Pressure Thresholds

• Systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on at least two separate occasions 1, 2
• Severity classification:
  • Mild: 140-159/90-109 mmHg 1
  • Severe: ≥160/110 mmHg (requires urgent management) 1

Timing Requirements

• Must develop after 20 weeks of gestation 1, 2
• This 20-week cutoff is pathophysiologically significant, reflecting when placental development and spiral artery remodeling should be complete 3
• Hypertension diagnosed before 20 weeks is classified as pre-existing (chronic) hypertension, not gestational 1, 2

Proteinuria Status

• Gestational hypertension occurs WITHOUT significant proteinuria 1
• When significant proteinuria develops (≥0.3 g/24h or ≥30 mg/mmol urinary creatinine in spot sample), the diagnosis changes to pre-eclampsia 1, 2

Clinical Characteristics

Natural History

• Resolves within 42 days postpartum in most cases 1
• If hypertension persists beyond 42 days postpartum, it should be reclassified as chronic hypertension 1
• Characterized by poor organ perfusion 1

Epidemiology

• Complicates 6-7% of pregnancies 1
• Accounts for a significant proportion of antenatal admissions 1

Important Clinical Distinctions

Differentiation from Other Hypertensive Disorders

The European Society of Cardiology guidelines emphasize that hypertension in pregnancy comprises four distinct entities 1:

1. Pre-existing (chronic) hypertension: BP ≥140/90 mmHg before pregnancy or before 20 weeks gestation, persisting >42 days postpartum 1, 2
2. Gestational hypertension: New-onset hypertension after 20 weeks without proteinuria 1
3. Pre-eclampsia: Gestational hypertension WITH significant proteinuria (≥0.3 g/24h) 1, 2
4. Pre-existing hypertension with superimposed gestational hypertension and proteinuria: Worsening BP and protein excretion ≥3 g/day after 20 weeks 1

Diagnostic Pitfalls

• Physiological BP fall in early pregnancy can mask pre-existing hypertension, making it appear as gestational hypertension when detected later 1
• Blood pressure normally falls approximately 15 mmHg in the second trimester before returning to baseline in the third trimester 1
• If BP is first recorded after 20 weeks, it is classified as "antenatally unclassifiable hypertension" and requires reassessment at or after 42 days postpartum 1

Measurement Recommendations

Diagnostic Confirmation

• Diagnosis requires at least two elevated BP readings on separate occasions 1, 2
• For severe hypertension (≥160/110 mmHg), confirmation should occur within 15 minutes due to emergency nature 2
• 24-hour ambulatory BP monitoring is superior to conventional measurements for predicting proteinuria, preterm delivery, and pregnancy outcomes 1, 2

Measurement Technique

• Use Korotkoff phase V (disappearance of sound) for diastolic BP measurement in pregnancy, not phase IV 1
• Phase V has better reproducibility despite historical preference for phase IV 1

Clinical Significance

Maternal and Fetal Risks

• Women with gestational hypertension face increased risk of progression to pre-eclampsia (up to 25% in those with pre-existing hypertension) 1
• Hypertensive disorders remain a major cause of maternal, fetal, and neonatal morbidity and mortality 2, 4
• Risks include abruptio placentae, cerebrovascular accidents, organ failure, intrauterine growth restriction, prematurity, and intrauterine death 2, 4

Emerging Evidence

• Recent research suggests that even blood pressure elevations of 130-139/80-89 mmHg after 20 weeks may indicate early disease, with 2.4-fold increased risk of developing hypertensive disorders 5
• This challenges current diagnostic thresholds, though guidelines have not yet changed 5