Preeclampsia & Hypertensive Disorders of Pregnancy
A Step 2 CK–focused lesson on the hypertensive-disorders-of-pregnancy spectrum — diagnostic criteria, severe features, magnesium prophylaxis, acute BP control, and delivery timing — built around the \"next best step\" the boards test.
The Spectrum & Why It Matters
Hypertensive disorders of pregnancy are defined relative to the 20-week gestational threshold and are a leading cause of maternal morbidity and mortality. The unifying lesion is abnormal placental spiral-artery remodeling → placental ischemia → release of anti-angiogenic factors (↑ sFlt-1, ↓ PlGF) → systemic endothelial dysfunction (vasospasm, capillary leak, end-organ ischemia). Because the placenta drives the disease, delivery is the only definitive cure.
On Step 2 CK the task is almost always two steps: (1) place the patient on the spectrum — chronic HTN, gestational HTN, preeclampsia ± severe features, eclampsia, HELLP — and (2) choose the next best step: workup vs. seizure prophylaxis vs. antihypertensive vs. delivery.
- HTN in pregnancy = BP ≥ 140/90 on two readings ≥ 4 h apart; severe-range = ≥ 160/110 (may be confirmed within minutes to expedite treatment).
- Onset < 20 wks → chronic HTN; new HTN ≥ 20 wks → gestational HTN or preeclampsia.
- Preeclampsia = new HTN ≥ 20 wks + proteinuria (≥ 300 mg/24 h, protein:creatinine ≥ 0.3, or dipstick 2+) OR new HTN + end-organ dysfunction even without proteinuria.
- Severe features (any ONE): SBP ≥ 160 or DBP ≥ 110; platelets < 100,000; AST/ALT ≥ 2× upper normal or severe/persistent RUQ/epigastric pain; Cr > 1.1 (or doubling); pulmonary edema; new headache unresponsive to meds and not otherwise explained; or visual disturbances.
- The degree of proteinuria is NOT a severe feature and does not by itself dictate delivery.
- Eclampsia = preeclampsia + generalized tonic-clonic seizure; can occur antepartum, intrapartum, or up to ~6 weeks postpartum.
Placing the Patient on the Spectrum
| Entity | Onset & BP | Proteinuria / labs | Boards hook |
|---|---|---|---|
| Chronic HTN | HTN < 20 wks or persists > 12 wks postpartum | Baseline; watch for superimposed preeclampsia | Continue safe agents (labetalol, nifedipine, methyldopa); avoid ACEi/ARB |
| Gestational HTN | New ≥ 140/90 at ≥ 20 wks | None; no severe features | Many progress — surveil closely; severe-range BP is managed like preeclampsia with severe features |
| Preeclampsia (no severe features) | New ≥ 140/90 at ≥ 20 wks | Proteinuria or end-organ dysfunction | Deliver at 37 wks |
| Preeclampsia w/ severe features | ≥ 160/110 or any severe-feature lab/symptom | ± proteinuria; ↓ plt, ↑ LFTs, ↑ Cr | MgSO₄ + antihypertensive; deliver ≥ 34 wks |
| Eclampsia | Any of above + seizure | — | Stabilize mother → MgSO₄ → deliver |
| HELLP | Often ≥ 160/110 but may be near-normal BP | Hemolysis, Elevated LFTs, Low Platelets | RUQ pain + hemolysis; deliver |
Classic vignette: A 33-year-old at 33 weeks presents with headache, blurred vision with scotomata, and RUQ pain. BP 166/113, brisk reflexes with clonus, 2+ pedal edema. Labs: platelets 88,000, AST 140.
Buzzwords → severe features: severe-range BP, headache, visual changes, RUQ/epigastric pain, thrombocytopenia, transaminitis, clonus.
NEXT BEST STEP: (in practice Mg and antihypertensive are started concurrently)
- IV magnesium sulfate for seizure prophylaxis (load ~ 4–6 g over 20–30 min, then 1–2 g/h).
- Acute antihypertensive for severe-range BP — IV labetalol, IV hydralazine, or PO immediate-release nifedipine. The goal is not to normalize BP but to bring it below the severe range (~140–150 / 90–100) to prevent maternal hemorrhagic stroke; over-correction risks placental hypoperfusion.
- Betamethasone for fetal lung maturity (gestation < 34 wks).
- Delivery — definitive treatment; with these labs (evolving HELLP), stabilize and proceed to delivery rather than prolonged expectant management.
Pitfall: Do not wait for proteinuria to diagnose or treat — end-organ dysfunction alone suffices.
HELLP — a severe variant of preeclampsia that can present even with only mildly elevated (or near-normal) BP:
- H — Hemolysis (microangiopathic: schistocytes, ↑ LDH, ↑ indirect bilirubin, ↓ haptoglobin)
- EL — Elevated Liver enzymes (↑ AST/ALT; RUQ/epigastric pain; risk of subcapsular hepatic hematoma)
- LP — Low Platelets (< 100,000)
Board pearl: HELLP + sudden RUQ pain, hypotension, and shock → suspect subcapsular liver hematoma or rupture. Management mirrors severe preeclampsia: MgSO₄, BP control, and delivery.
- Definitive treatment = delivery of the placenta; everything else is temporizing.
- MgSO₄ = seizure prophylaxis (severe features) and first-line treatment of eclamptic seizures — superior to diazepam/phenytoin. It is NOT an antihypertensive.
- Acute severe-range BP (≥ 160/110): IV labetalol, IV hydralazine, or PO immediate-release nifedipine — treat as soon as feasible (ideally within ~30–60 min) to prevent stroke.
- Avoid ACE inhibitors/ARBs (fetal renal dysgenesis/oligohydramnios) and nitroprusside (fetal cyanide) in pregnancy.
- Delivery timing: gestational HTN / preeclampsia without severe features → 37 wks; with severe features → ≥ 34 wks (earlier if unstable). If < 34 wks and stable, expectant management + betamethasone at a capable center.
- Prevention: low-dose aspirin 81 mg/day for high-risk women, started 12–28 wks (ideally before 16 wks), continued until delivery.
- Postpartum: disease can appear or worsen up to ~6 wks postpartum; continue MgSO₄ for ~24 h after delivery or the last seizure.
Eclamptic seizure — NEXT BEST STEP: The convulsion is usually self-limited; do not rush to deliver during the seizure.
- Protect the airway — left lateral decubitus, O₂, IV access (ABCs).
- IV magnesium sulfate (load + infusion) — first-line even for active seizures; recurrent seizure → additional 2–4 g IV bolus.
- Control severe-range BP (labetalol / hydralazine).
- Deliver AFTER maternal stabilization — regardless of gestational age.
Magnesium toxicity (Mg is renally cleared) — recognize the ascending sequence:
- Loss of deep tendon reflexes (earliest) → respiratory depression → cardiac arrest.
- NEXT BEST STEP: stop the infusion and give IV calcium gluconate; monitor reflexes, respiratory rate, and urine output; reduce dose in renal insufficiency.
Thrombocytopenia in the 3rd Trimester — Don't Miss the Mimics
| Condition | Distinguishing feature | Hallmark labs |
|---|---|---|
| HELLP | HTN/proteinuria + RUQ pain; 3rd trimester or postpartum | Hemolysis, ↑ AST/ALT, plt < 100k |
| AFLP (acute fatty liver of pregnancy) | Malaise, N/V, hypoglycemia, encephalopathy | ↑↑ transaminases, DIC, ↑ ammonia, ↑ bilirubin, low glucose |
| TTP | Neuro deficits + fever; hemolysis-dominant; may present earlier | ADAMTS13 < 10%, normal LFTs/coags, ↑↑ LDH |
| HUS | Renal failure predominant; often postpartum | ↑↑ Cr, hemolysis, thrombocytopenia |
| ITP | Isolated low platelets; can be earlier/more severe; no hemolysis or HTN | Normal LFTs, LDH, coags |
| Gestational thrombocytopenia | Most common cause in pregnancy; mild, asymptomatic, late 3rd trimester; no HTN | Platelets usually > 70k; normal LFTs/LDH/coags; resolves postpartum |
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