Diagnosing Hypertensive Disorders of Pregnancy
Diagnose each hypertensive disorder by determining the timing of hypertension onset (before or after 20 weeks' gestation) and the presence or absence of maternal organ dysfunction or proteinuria, using BP ≥140/90 mmHg as the diagnostic threshold. 1
Core Diagnostic Framework
The diagnosis hinges on two critical decision points: when the hypertension appeared and what additional features are present. This algorithmic approach allows you to systematically classify each disorder.
Step 1: Establish Blood Pressure Criteria
- Hypertension is defined as BP ≥140 mmHg systolic OR ≥90 mmHg diastolic 1
- Severe hypertension: BP ≥160 mmHg systolic OR ≥110 mmHg diastolic 1
- Confirm severe BP within 15 minutes; for non-severe elevations, repeat measurements over several hours 1
Critical pitfall: A normal BP first measured after 12 weeks' gestation may reflect the physiologic first-trimester BP fall, masking underlying chronic hypertension. You need documented normal BP either prepregnancy or in early pregnancy (before 12 weeks) to confidently exclude chronic hypertension. 1
Step 2: Determine Timing of Hypertension Onset
This is your primary branching point:
Before 20 Weeks or Known Pre-pregnancy = Chronic Hypertension
- Hypertension documented before pregnancy or present in first 20 weeks 1
- Most cases are essential hypertension (family history, obesity common) 1
- Secondary causes (renal disease, fibromuscular dysplasia, primary hyperaldosteronism) are uncommon; don't routinely test unless clinical clues present 1
Mandatory baseline testing at diagnosis (to detect superimposed preeclampsia later, which occurs in up to 25% of cases): 1
- Complete blood count (hemoglobin, platelets)
- Liver enzymes (AST, ALT, LDH) and function tests (INR, bilirubin, albumin)
- Serum creatinine, electrolytes, uric acid
- Urinalysis with microscopy, plus protein-to-creatinine ratio (PCR) or albumin-to-creatinine ratio
- Renal ultrasound if creatinine or urine testing abnormal
Special considerations:
- White-coat hypertension: Elevated clinic BP but normal at other times; confirm with 24-hour ambulatory BP monitoring (ABPM) or home BP monitoring before diagnosing true chronic hypertension 1
- Masked hypertension: Normal clinic BP but elevated elsewhere; only seek this diagnosis if unexplained target organ damage (CKD, left ventricular hypertrophy, retinopathy) present early in pregnancy 1
At or After 20 Weeks = Gestational Hypertension, Transient Gestational Hypertension, or Preeclampsia
This is where you must differentiate three distinct entities:
Step 3: Classify Hypertension Arising After 20 Weeks
Transient Gestational Hypertension
- Hypertension detected in clinic that resolves with repeated measurements over several hours (e.g., in day assessment unit) 1
- Differs from white-coat hypertension (which must be present from early pregnancy)
- Not benign: 40% risk of developing true gestational hypertension or preeclampsia later 1
- Requires close monitoring throughout pregnancy, ideally with home BP measurements 1
Gestational Hypertension
- Persistent de novo hypertension at or after 20 weeks without features of preeclampsia 1
- No proteinuria, no maternal organ dysfunction, no fetal involvement
- Risk of complications depends on gestational age at onset (earlier = higher risk)
Preeclampsia
Preeclampsia is gestational hypertension PLUS ≥1 of the following new-onset conditions at or after 20 weeks: 1
Maternal Organ Dysfunction:
- Renal: Creatinine ≥90 μmol/L (1.02 mg/dL), or other renal impairment
- Hepatic: Elevated transaminases (AST or ALT), with or without right upper quadrant/epigastric pain
- Hematologic: Thrombocytopenia (platelets <150,000/μL), disseminated intravascular coagulation, hemolysis
- Neurologic: New headache (unresponsive to medication, not explained by alternative diagnosis), visual disturbances (scotomata, cortical blindness), stroke, seizure (eclampsia), altered mental status, clonus
- Pulmonary edema
OR Proteinuria:
- Spot urine PCR ≥30 mg/mmol OR albumin-to-creatinine ratio ≥8 mg/mmol
- 24-hour urine protein ≥300 mg
- Dipstick ≥2+ (if quantitative methods unavailable)
Note: Proteinuria is present in only ~75% of preeclampsia cases and is not required for diagnosis 1
OR Uteroplacental Dysfunction:
- Fetal growth restriction
- Abnormal umbilical artery Doppler waveform analysis
- Stillbirth
HELLP Syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets): This is not a separate disorder—it represents preeclampsia with specific severe features. Manage as preeclampsia and seek all other features of the condition. 1
Important: The term "severe preeclampsia" should not be used in clinical practice, as preeclampsia can become life-threatening at any stage regardless of initial classification. Instead, describe preeclampsia with or without severe features. 1
Step 4: Identify Superimposed Preeclampsia
Preeclampsia superimposed on chronic hypertension occurs when a woman with chronic hypertension develops new features of preeclampsia at or after 20 weeks 1
Diagnostic challenge: This is why baseline testing at chronic hypertension diagnosis is critical—you need reference values to detect new organ dysfunction.
Look for:
- New or worsening proteinuria
- New maternal organ dysfunction (as listed above)
- New fetal growth restriction or abnormal Dopplers
Step 5: Handle Unknown Baseline BP
When a woman presents with hypertension at or after 20 weeks and earlier BP is unknown: Manage her as if she has gestational hypertension or preeclampsia during pregnancy. Perform postpartum investigations to determine if underlying chronic hypertension exists—BP will not normalize within 3 months postpartum if chronic hypertension is present. 1
Essential Laboratory Workup for All New Hypertension After 20 Weeks
To exclude preeclampsia, you must perform same-day laboratory investigations when resources available: 1
- Complete blood count
- Liver enzymes and function tests
- Serum creatinine, electrolytes, uric acid (elevated gestation-corrected uric acid associated with worse outcomes but not diagnostic)
- Quantitative proteinuria assessment (PCR or albumin-to-creatinine ratio)
Without these tests, you cannot exclude preeclampsia. In resource-limited settings where same-day labs are unavailable, referral may be necessary. 1
Key Clinical Pitfalls to Avoid
Don't rely on hyperreflexia: It's nonspecific, present in many healthy young women, and highly subject to observer interpretation—no longer recommended as diagnostic criterion 1
Don't dismiss new headache: In the presence of hypertension, treat any new headache as preeclampsia until proven otherwise 1
Don't wait for proteinuria: 25% of preeclampsia cases lack proteinuria; organ dysfunction alone is sufficient for diagnosis 1
Don't use uric acid to time delivery: While elevated levels indicate worse prognosis, they should not determine delivery timing 1
Validate home BP devices: ~25% of automated devices differ from standard sphygmomanometry; check all home devices against calibrated equipment before relying on readings 1
Use appropriate BP measurement technique: Liquid crystal sphygmomanometers are preferred; if using automated devices, ensure validation specifically for pregnancy and preeclampsia 1