What are the criteria for diagnosing hypertension in pregnancy?

Criteria for Diagnosing Hypertension in Pregnancy

Hypertension in pregnancy is defined as systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg, measured on at least two separate occasions. 1, 2

Classification of Hypertensive Disorders in Pregnancy

Hypertensive disorders in pregnancy are classified into four main categories:

1. Pre-existing (Chronic) Hypertension

• Defined as hypertension (≥140/90 mmHg) that either predates pregnancy or develops before 20 weeks of gestation 1, 2
• Usually persists >42 days post-partum 1
• May be associated with proteinuria 1
• Complicates 1-5% of pregnancies 1
• Important note: Normal physiological BP fall in the first trimester may mask pre-existing hypertension, making it appear as gestational hypertension when detected later 1

2. Gestational Hypertension

• New-onset hypertension (≥140/90 mmHg) that develops at or after 20 weeks' gestation 1
• Resolves in most cases within 42 days post-partum 1
• Characterized by poor organ perfusion 1
• Complicates 6-7% of pregnancies 1
• Transient gestational hypertension (hypertension that settles with repeated BP readings) carries a 40% risk of developing true gestational hypertension or preeclampsia later in pregnancy 1, 2

3. Pre-eclampsia

• Gestational hypertension with significant proteinuria (≥0.3 g/day in 24h urine collection or ≥30 mg/mmol urinary creatinine in a spot sample) 1
• A systemic disorder with both maternal and fetal manifestations 1
• Complicates 5-7% of pregnancies, but increases to 25% in women with pre-existing hypertension 1
• More frequent during first pregnancy, multiple fetuses, hydatidiform mole, or diabetes 1

4. Pre-existing Hypertension with Superimposed Gestational Hypertension and Proteinuria

• Pre-existing hypertension with further worsening of BP and protein excretion ≥3 g/day in 24h urine collection after 20 weeks gestation 1

5. Antenatally Unclassifiable Hypertension

• When BP is first recorded after 20 weeks gestation and hypertension is diagnosed 1
• Should be managed as gestational hypertension or preeclampsia during pregnancy 1, 2
• Re-assessment is necessary at or after 42 days post-partum to determine final classification 1

Diagnostic Criteria and Measurement

Blood Pressure Measurement

• Diagnosis should be based on at least two high BP readings on two separate occasions 1
• For severe hypertension (≥160/110 mmHg), confirmation should be done within 15 minutes 1, 2
• For less severe hypertension, repeated readings should be taken over several hours 1, 2
• Use a liquid crystal sphygmomanometer if available; if not, use a validated and appropriately calibrated automated device 1
• Korotkoff phase V (disappearance of sound) is now recommended for diastolic BP measurement 1
• 24-hour ambulatory BP monitoring is superior to conventional measurements for predicting outcomes and may be useful for diagnosis, particularly in high-risk pregnant women 1

Severity Classification

• Mild to moderate hypertension: 140-159/90-109 mmHg 1
• Severe hypertension: ≥160/110 mmHg 1, 2

Special Considerations

• White-coat hypertension: elevated clinic BP but normal home or ambulatory BP 2
• Masked hypertension: normal clinic BP but elevated BP at other times 1, 2
• Transient gestational hypertension: hypertension that settles with repeated BP readings 1

Proteinuria Assessment

• Proteinuria should be initially assessed by automated dipstick urinalysis when possible 1
• Significant proteinuria is defined as:
  • ≥0.3 g/day in a 24h urine collection 1
  • ≥30 mg/mmol urinary creatinine in a spot random urine sample 1
  • Dipstick 2+ or more 1

Common Pitfalls in Diagnosis

• Failing to document normal BP in early pregnancy (before 12 weeks) may make it difficult to differentiate between chronic and gestational hypertension 1
• The physiological BP fall in the first trimester may mask pre-existing hypertension 1
• Using incorrect BP measurement techniques or equipment can lead to misdiagnosis 1
• Aneroid devices may be inaccurate and need regular calibration 1
• Not all automated devices validated for general use are accurate in preeclampsia 1
• Transient gestational hypertension should not be dismissed as it carries significant risk for developing true gestational hypertension or preeclampsia 1, 2

Clinical Implications

• Hypertensive disorders in pregnancy remain a major cause of maternal, fetal, and neonatal morbidity and mortality 1, 3
• Women with hypertension in pregnancy are at higher risk for severe complications including abruptio placentae, cerebrovascular accidents, organ failure, and disseminated intravascular coagulation 1
• The fetus is at risk for intrauterine growth restriction, prematurity, and intrauterine death 1
• Proper diagnosis and classification are essential for appropriate management and follow-up 2, 4