How is preeclampsia diagnosed in a pregnant woman at ≥20 weeks gestation?

How to Diagnose Preeclampsia

Preeclampsia is diagnosed by new-onset hypertension (BP ≥140/90 mmHg) at or after 20 weeks' gestation accompanied by either proteinuria OR evidence of maternal organ dysfunction OR uteroplacental dysfunction. 1

Blood Pressure Criteria

The hypertension threshold is clear and must be confirmed:

• Systolic BP ≥140 mmHg and/or diastolic BP ≥90 mmHg
• If BP is severe (≥160/110 mmHg), confirm within 15 minutes
• For non-severe elevations, repeat measurements over several hours 1

Critical timing point: The 20-week gestational age cutoff is essential—any hypertension before 20 weeks is classified as chronic hypertension, not preeclampsia 1

Diagnostic Components Beyond Hypertension

Proteinuria is NOT required for diagnosis (present in only ~75% of cases), but when present helps confirm the diagnosis 1:

• ≥0.3 g/24-hour urine collection, OR
• Protein:creatinine ratio ≥30 mg/mmol 2

Maternal Organ Dysfunction Criteria

In the absence of proteinuria, preeclampsia is diagnosed if ANY of the following are present 1:

Laboratory Evidence:

• Thrombocytopenia (low platelets)
• Elevated liver enzymes (AST, ALT, LDH) with or without hemolysis
• Renal insufficiency (elevated serum creatinine)
• Elevated uric acid (though not diagnostic alone, it indicates worse outcomes) 1

Clinical Manifestations:

• New-onset headache (in presence of hypertension, consider preeclampsia until proven otherwise) 1
• Visual disturbances
• Pulmonary edema
• Right upper quadrant or epigastric pain

Uteroplacental Dysfunction:

• Fetal growth restriction in the context of new-onset gestational hypertension should be considered preeclampsia even without other maternal features 1

Essential Laboratory Workup

All women with new-onset hypertension after 20 weeks require the following investigations to exclude preeclampsia 1:

1. Complete blood count (hemoglobin, platelet count)
2. Liver function tests (AST, ALT, LDH, bilirubin, albumin, INR)
3. Renal function (creatinine, electrolytes, uric acid)
4. Urine assessment (urinalysis, microscopy, protein:creatinine ratio or albumin:creatinine ratio)
5. Renal ultrasound if creatinine or urine testing abnormal

Without these laboratory tests, it is impossible to exclude preeclampsia 1

Important Clinical Pitfalls

HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) is not a separate disorder—it represents preeclampsia with severe features and should be managed as such 1

Avoid the term "severe preeclampsia" 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

Hyperreflexia is no longer recommended as a diagnostic criterion due to poor specificity and high inter-observer variability 1

Biomarkers (Emerging but Not Required)

While sFlt-1/PlGF ratio shows promise for risk assessment and has FDA approval for this purpose 3, current guidelines do not recommend routine use solely to reduce maternal or perinatal morbidity 2. These biomarkers may help in uncertain cases but are not part of standard diagnostic criteria 4, 3.

Diagnostic Algorithm Summary

1. Confirm hypertension ≥140/90 mmHg at or after 20 weeks
2. Assess for proteinuria (dipstick, then quantify if positive)
3. If no proteinuria: Obtain complete laboratory panel immediately
4. Diagnose preeclampsia if: Proteinuria present OR any organ dysfunction OR fetal growth restriction
5. Assess for severe features: BP ≥160/110, symptoms (headache, visual changes, RUQ pain), laboratory abnormalities