Diagnostic Criteria for Chronic Hypertension in Pregnancy
Chronic hypertension in pregnancy is diagnosed when blood pressure is ≥140/90 mmHg either documented before pregnancy OR first identified before 20 weeks of gestation. 1, 2
Blood Pressure Thresholds
- Systolic BP ≥140 mmHg OR diastolic BP ≥90 mmHg defines hypertension in pregnancy, which differs from the lower thresholds used in non-pregnant adults 1, 2
- Measurements must be confirmed on at least two separate occasions to establish the diagnosis 2, 3
- For severe hypertension (≥160/110 mmHg), confirmation should occur within 15 minutes, while less severe elevations require repeated measurements over several hours or on 2 consecutive visits 3, 4
Timing Criteria: The 20-Week Rule
The critical distinction for chronic hypertension is the 20-week gestational age cutoff: 1, 2
- Before 20 weeks = Chronic hypertension
- At or after 20 weeks = Gestational hypertension
If a woman has documented hypertension before conception, this automatically qualifies as chronic hypertension regardless of pregnancy BP readings 2
Confirmation Methods Beyond Office Readings
Elevated office BP should not stand alone as diagnostic evidence. The American Society of Hypertension recommends confirmation through: 2
- 24-hour ambulatory BP monitoring (ABPM) - considered superior for predicting outcomes 3
- Home BP monitoring - diagnostic threshold is ≥135/85 mmHg (lower than office threshold) 2
- Repeated office measurements - minimum of 2 readings at least 4 hours apart 1
Important Caveat on White-Coat Hypertension
Office BP ≥140/90 mmHg with normal home/ambulatory readings (<135/85 mmHg) is not entirely benign and still conveys increased risk for preeclampsia, warranting closer monitoring 2, 4
Essential Baseline Testing at Diagnosis
Once chronic hypertension is confirmed, obtain baseline laboratory studies to facilitate later detection of superimposed preeclampsia: 2, 4
- Complete blood count
- Liver enzymes (AST, ALT)
- Serum creatinine and electrolytes
- Uric acid
- Proteinuria assessment (24-hour urine or spot protein-to-creatinine ratio)
Clinical Significance and Risk Stratification
Women with chronic hypertension face substantially elevated risks: 1
- Superimposed preeclampsia occurs in a significant proportion, with stroke risk of 1 in 370 deliveries (compared to 1 in 5000 without hypertension)
- Sustained BP >140/90 mmHg carries a pooled risk ratio of 2.64 for maternal stroke compared to BP <120/80 mmHg 1
Common Pitfall to Avoid
Do not dismiss BP readings in the 120-139/80-89 mmHg range as entirely normal. While not meeting diagnostic criteria for chronic hypertension, this range before 20 weeks carries a 2.85-fold increased risk of developing hypertensive disorders later in pregnancy compared to BP <120/80 mmHg 5