Preeclampsia vs Eclampsia: How to Tell Them Apart
Preeclampsia and eclampsia are points on the same hypertensive-disorder-of-pregnancy spectrum, sharing an origin in abnormal placentation, endothelial dysfunction, and vasospasm. The single axis that separates them is the seizure: eclampsia is defined as generalized tonic-clonic seizures occurring in a patient with preeclampsia, with no other cause. Recognizing where a patient sits on this spectrum drives the urgency of magnesium and delivery.
How to tell them apart
| Feature | Preeclampsia | Eclampsia |
|---|---|---|
| Defining criterion | Hypertension (BP ≥140/90 on two occasions ≥4 hours apart after 20 weeks) PLUS proteinuria, or in its absence, end-organ damage | Preeclampsia complicated by new generalized tonic-clonic seizures with no other identifiable cause |
| Seizures | Absent; patient may have cerebral/visual symptoms and hyperreflexia with clonus but has not convulsed | Present — generalized tonic-clonic seizures are the hallmark |
| Severity implication | Ranges from without severe features to with severe features (severe-range BP ≥160/110, thrombocytopenia, elevated transaminases, cerebral/visual symptoms) | Represents a severe, life-threatening progression of the disease |
| Role of magnesium sulfate | Used for seizure prophylaxis, particularly with severe features | Used as first-line treatment to stop and prevent recurrent seizures |
| Immediate priorities | Blood pressure control, seizure prophylaxis, and planning delivery based on gestational age and severity | Protect the airway, position the patient on her side, give magnesium sulfate, control severe hypertension, then prepare for delivery once stabilized |
| Timing of presentation | Diagnosed on hypertension plus proteinuria/end-organ criteria after 20 weeks; managed expectantly or by delivery depending on gestational age | Roughly half antepartum, a quarter during labor, and a quarter postpartum (up to 6 weeks, most within 48 hours) |
| Urgency of delivery | Timing depends on gestational age and severe features — deliver at 37 weeks if without severe features, and at ≥34 weeks if with severe features | Delivery is prepared once the patient is stabilized after seizure control, regardless of stage |
The reasoning
Anchor on the seizure. A patient with hypertension after 20 weeks plus proteinuria or end-organ damage (thrombocytopenia, liver dysfunction, renal insufficiency, pulmonary edema, or cerebral/visual symptoms) has preeclampsia — note that BP elevation alone, without these, is only gestational hypertension. Severe-range BP (≥160/110 mmHg) marks severe features and demands prompt antihypertensive therapy. The moment a preeclamptic patient has a generalized tonic-clonic seizure with no other cause, the diagnosis becomes eclampsia. Warning signs of impending eclampsia — headache, visual symptoms like 'seeing spots,' and hyperreflexia with clonus — indicate preeclampsia with severe features at high risk, but until a convulsion occurs it remains preeclampsia. Magnesium sulfate is the common thread: prophylactic in severe preeclampsia, therapeutic in eclampsia. In both, stabilize first, then deliver.
Key tests
- Blood pressure measurement: elevated in both. BP ≥140/90 on two occasions ≥4 hours apart after 20 weeks establishes hypertension, but preeclampsia requires this PLUS proteinuria or end-organ damage; BP alone reflects gestational hypertension. Severe-range BP (≥160/110 mmHg, confirmable within minutes rather than waiting 4 hours) defines severe features, mandates urgent antihypertensive treatment, and raises the risk of progression to eclampsia
- Proteinuria assessment (24-hour protein ≥300 mg, protein/creatinine ratio ≥0.3, or dipstick): supports the preeclampsia diagnosis; not required if end-organ damage is present
- End-organ labs (platelets, transaminases, LDH, renal function): thrombocytopenia, elevated transaminases, and elevated LDH define severe preeclampsia and flag risk of eclampsia and HELLP; these do not distinguish eclampsia, which is diagnosed clinically by the seizure
What they share
- Both arise from the same pathophysiology: abnormal placentation, placental ischemia with release of anti-angiogenic factors, systemic endothelial dysfunction, and vasospasm causing end-organ damage
- Both feature hypertension after 20 weeks and can involve cerebral/visual symptoms such as headache and visual disturbance
- Magnesium sulfate is central to both — for prophylaxis in severe preeclampsia and as first-line treatment in eclampsia
- Delivery is the only definitive cure for both once the patient is stabilized
- Both can occur antepartum, intrapartum, or postpartum
Pitfalls
- Assuming BP elevation alone establishes preeclampsia — hypertension without proteinuria or end-organ damage is gestational hypertension, not preeclampsia
- Assuming proteinuria is mandatory — preeclampsia can be diagnosed without it when end-organ damage (thrombocytopenia, liver or renal dysfunction, pulmonary edema, or cerebral/visual symptoms) is present
- Waiting the full 4-hour interval to confirm severe-range BP (≥160/110) — this threshold can be confirmed within minutes and requires prompt antihypertensive treatment
- Treating hyperreflexia, clonus, headache, or visual symptoms as eclampsia — these are severe features and warning signs, but eclampsia requires an actual seizure
- Forgetting that eclampsia (and preeclampsia) can present postpartum, up to 6 weeks after delivery and most within 48 hours
- Dropping blood pressure too fast or too low — placental perfusion depends on maternal BP, so target controlled reduction rather than normalization
- Overlooking magnesium toxicity during treatment — loss of patellar reflexes, respiratory depression, and oliguria signal excess; calcium gluconate is the antidote
Practice this the way the exam tests it — on branching cases where your decisions shape the patient.