How is pre‑eclampsia diagnosed in a pregnant patient beyond 20 weeks gestation?

How to Diagnose Pre-eclampsia

Pre-eclampsia is diagnosed after 20 weeks of gestation by the presence of new-onset hypertension (≥140/90 mmHg confirmed on two occasions at least 15 minutes apart) combined with either proteinuria (≥300 mg/24h or ≥+ on dipstick on more than one occasion) OR evidence of maternal organ dysfunction in the absence of proteinuria. 1

Core Diagnostic Requirements

Timing and Blood Pressure Criteria

• Pre-eclampsia cannot be diagnosed before 20 weeks of gestation (except in rare cases such as molar pregnancy or fetal triploidy) 2, 1
• New-onset hypertension must be documented: systolic BP ≥140 mmHg and/or diastolic BP ≥90 mmHg 1
• Blood pressure elevation must be confirmed on two separate occasions at least 15 minutes apart 1
• The patient must have been previously normotensive, with documented normal BP before 20 weeks or in early pregnancy 2, 1

Primary Diagnostic Pathway: Hypertension + Proteinuria

• Proteinuria is defined as ≥300 mg in a 24-hour urine collection 1
• Alternatively, proteinuria can be detected as ≥+ on dipstick on more than one occasion 3, 2
• This traditional combination of hypertension plus proteinuria remains the most straightforward diagnostic approach 1

Alternative Diagnostic Pathway: Hypertension + Organ Dysfunction (When Proteinuria is Absent)

When proteinuria is not present, pre-eclampsia can still be diagnosed if gestational hypertension is accompanied by ANY ONE of the following maternal organ dysfunctions 1:

Renal dysfunction:

• Serum creatinine ≥1.1 mg/dL or doubling of baseline creatinine 1

Hepatic dysfunction:

• Liver transaminases ≥2× upper limit of normal 2
• Severe persistent right upper quadrant or epigastric pain 2

Hematological dysfunction:

• Platelet count <100,000/µL 2
• Progressive thrombocytopenia 1

Neurological complications:

• New cerebral or visual symptoms (persistent severe headache, visual disturbances such as blurred vision, scotomata, photophobia) 2, 1
• Hyperreflexia and clonus 4

Pulmonary complications:

• Pulmonary edema 1

Uteroplacental dysfunction:

• Reduced fetal movements reported by the patient 3, 2
• Small-for-gestational-age infant on ultrasound 3, 2
• Non-reassuring fetal status 1

Clinical Assessment Protocol After 20 Weeks

At every antenatal assessment after 20 weeks, actively screen for the following signs and symptoms 3:

• New hypertension (measure BP at every visit) 3
• New proteinuria (dipstick urinalysis at every visit) 3
• Headache or visual disturbance (persistent, severe headache unresponsive to usual treatment; blurred vision, scotomata, photophobia) 3, 2
• Epigastric pain or vomiting (severe or persistent right upper quadrant/epigastric pain; new-onset vomiting after 20 weeks) 3, 2
• Reduced fetal movements 3, 2
• Small-for-gestational-age infant 3

Laboratory Evaluation When Pre-eclampsia is Suspected

When clinical suspicion arises, obtain the following tests 1:

• Complete blood count (to assess platelet count and hemolysis)
• Liver enzymes (AST, ALT)
• Serum creatinine and electrolytes
• Uric acid
• Urinalysis with protein quantification (24-hour urine collection or protein-to-creatinine ratio)

The sFlt-1/PlGF ratio ≤38 can exclude development of pre-eclampsia in the following week when clinically suspected 1, which is particularly useful in ambiguous cases.

Severity Classification: Pre-eclampsia with Severe Features

Pre-eclampsia with severe features is diagnosed when ANY of the following are present 2, 1:

• Severe hypertension: BP ≥160/110 mmHg 2
• Severe persistent right upper quadrant or epigastric pain 2
• Serum creatinine >1.1 mg/dL or doubling of baseline 2
• Platelet count <100,000/µL 2
• Liver transaminases ≥2× upper limit of normal 2
• New cerebral or visual symptoms unresponsive to treatment 2
• Pulmonary edema 1
• Non-reassuring fetal status 1

Critical pitfall: Proteinuria does NOT define the severity of preeclampsia—even a single severe feature mandates management as severe disease regardless of proteinuria level 2

Referral Thresholds Based on Findings

Diastolic BP ≥90 and <100 mmHg without proteinuria:

• Refer for hospital assessment within 48 hours 1

Diastolic BP ≥90 and <100 mmHg with proteinuria ≥+ on dipstick:

• Refer for same-day hospital assessment 1

Any severe feature present:

• Immediate referral and management as severe pre-eclampsia 2, 1

Important Clinical Pitfalls

• Transient gestational hypertension (BP elevations that resolve on repeat measurement) carries approximately 40% risk of progressing to true gestational hypertension or pre-eclampsia, requiring close follow-up with home BP monitoring 2
• HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) represents the severe end of the pre-eclampsia spectrum and requires immediate delivery consideration 2
• Atypical presentations can occur before 20 weeks (with molar pregnancy) or beyond 48 hours postpartum, requiring heightened clinical suspicion 5, 6
• Eclampsia can still occur postpartum, so continued vigilance is necessary even after delivery 4

Postpartum Pre-eclampsia

Pre-eclampsia can be diagnosed postpartum as new-onset hypertension (≥140/90 mmHg) occurring 48 hours to 6 weeks after delivery with either proteinuria or maternal organ dysfunction 1. Blood pressure should be monitored at least every 4 hours while awake for at least 3 days postpartum 1, 4.