Preeclampsia — Diagnosis, HELLP Syndrome & Management

Q: What is the mechanism and dosing of magnesium sulfate for eclampsia prophylaxis?

Magnesium sulfate is the drug of choice for both prevention and treatment of eclamptic seizures. It works via CNS vasodilation, N-methyl-D-aspartate (NMDA) receptor antagonism, and anticonvulsant effects. Dosing: 4–6g IV loading dose over 15–20 minutes, then 1–2 g/hr continuous infusion during labor and 24 hours postpartum. Monitor for toxicity every hour: patellar reflex loss (first sign, Mg 7–10 mEq/L), respiratory rate 25 mL/hr. Antidote: calcium gluconate 1g IV.

The 60-second version

Preeclampsia: BP ≥140/90 at ≥20 weeks + proteinuria OR end-organ damage (proteinuria no longer required)
Severe features: BP ≥160/110, platelets <100K, creatinine >1.1, liver enzymes >2×, pulmonary edema, neuro symptoms
Magnesium sulfate for seizure prophylaxis; antidote = calcium gluconate; monitor reflexes/respirations
HELLP: Hemolysis + Elevated Liver enzymes + Low Platelets — deliver at any gestational age if unstable
Definitive treatment = delivery; give steroids for fetal lung maturity if 24–34 weeks before delivery

Diagnostic Criteria

Preeclampsia: new-onset hypertension (BP ≥140/90 on two occasions ≥4h apart) at ≥20 weeks gestation PLUS one of: proteinuria (≥300 mg/24h OR protein:creatinine ratio ≥0.3 OR dipstick ≥2+), thrombocytopenia (<100,000), renal insufficiency (creatinine >1.1 or doubling), impaired liver function (AST/ALT >2× normal or severe RUQ/epigastric pain), pulmonary edema, or new-onset headache unresponsive to medication. Note: proteinuria is NO LONGER required for diagnosis — other end-organ criteria suffice. Gestational hypertension: HTN after 20 weeks WITHOUT other criteria. Chronic HTN: HTN diagnosed before 20 weeks or pre-pregnancy. Superimposed preeclampsia: preeclampsia in a woman with chronic HTN — worsened HTN + new proteinuria/end-organ damage.

Severe Features

Any of the following = preeclampsia with severe features: BP ≥160/110 on two occasions ≥4h apart (or ≥15 min if antihypertensives needed urgently), thrombocytopenia <100,000, creatinine >1.1 or doubling, 2× normal transaminases + RUQ pain, pulmonary edema, new-onset headache OR visual changes (scotomata, blurring — from cerebral vasospasm). Delivery: without severe features at ≥37 weeks; WITH severe features at ≥34 weeks (if maternal or fetal condition is stable, some centers deliver at 34 weeks; unstable = immediate delivery at any gestational age). IV antihypertensives for BP ≥160/110: labetalol IV, hydralazine IV, or oral nifedipine — target 140–155/90–100 (avoid excessive lowering = fetal hypoperfusion).

Magnesium and HELLP Syndrome

Magnesium sulfate: given IV for seizure prophylaxis in preeclampsia with severe features during labor and 24h postpartum. Mechanism: CNS vasodilation, anticonvulsant. Signs of Mg toxicity (rising levels): loss of patellar reflexes (first sign, at Mg 7–10), respiratory depression (Mg >10–13), cardiac arrest (Mg >15). Monitor: hourly urine output (>25 mL/hr), patellar reflexes, respiratory rate. Antidote: calcium gluconate IV. HELLP syndrome: Hemolysis (LDH elevated, schistocytes) + Elevated Liver enzymes (AST/ALT >2×) + Low Platelets (<100,000). A severe variant of preeclampsia. Delivery is definitive treatment at any gestational age if unstable. DIC is a complication — monitor coagulation. Eclampsia: new-onset tonic-clonic seizures in a preeclamptic patient (or within 48h postpartum). Treatment: magnesium sulfate (both treatment and prophylaxis); if seizure during Mg infusion, give extra Mg bolus; only use benzodiazepines if Mg fails. Deliver after stabilization.

Test yourself

Quick check — 3 questions

1. A 34-week pregnant woman has BP 170/115 on two readings, headache, and RUQ pain. AST 210 U/L, platelets 88,000. She has HELLP syndrome. The most appropriate management is:

2. A laboring patient on magnesium infusion for preeclampsia develops absent patellar reflexes and respiratory rate of 9 breaths/min. The immediate intervention is:

3. Which of the following findings is sufficient to diagnose preeclampsia WITHOUT proteinuria?

Frequently asked questions

What is the mechanism and dosing of magnesium sulfate for eclampsia prophylaxis?

Magnesium sulfate is the drug of choice for both prevention and treatment of eclamptic seizures. It works via CNS vasodilation, N-methyl-D-aspartate (NMDA) receptor antagonism, and anticonvulsant effects. Dosing: 4–6g IV loading dose over 15–20 minutes, then 1–2 g/hr continuous infusion during labor and 24 hours postpartum. Monitor for toxicity every hour: patellar reflex loss (first sign, Mg 7–10 mEq/L), respiratory rate <12, urine output >25 mL/hr. Antidote: calcium gluconate 1g IV.

How does preeclampsia differ from chronic hypertension in pregnancy?

Chronic hypertension in pregnancy is diagnosed when HTN is present before 20 weeks of gestation or before pregnancy. Preeclampsia is new-onset HTN at ≥20 weeks PLUS end-organ involvement. Women with chronic HTN can develop superimposed preeclampsia (new proteinuria, worsening HTN, or new end-organ damage on a background of chronic HTN). Chronic HTN alone does not meet the threshold for magnesium or urgent delivery unless preeclampsia superimposes. Managing blood pressure in chronic HTN in pregnancy: target <160/110; labetalol, nifedipine, or methyldopa (not ACEi/ARBs — teratogenic).

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