Preeclampsia and Magnesium Sulfate

Maternal & Newborn · High-Risk Pregnancy (Preeclampsia, GDM)·Updated 2026-10-28

What it is

Preeclampsia is new hypertension after 20 weeks of gestation with proteinuria or signs of end-organ dysfunction. Abnormal placentation causes widespread endothelial damage and vasospasm, which reduce perfusion to the kidneys, liver, brain and placenta. Magnesium sulfate is a central nervous system depressant that prevents and treats eclamptic seizures; it is not an antihypertensive. Birth of the placenta is the only cure.

What the NCLEX focuses on

Severe features: blood pressure of 160 systolic or 110 diastolic or higher, platelets below 100,000/mm3, liver enzymes twice normal or severe right upper quadrant or epigastric pain, creatinine above 1.1 mg/dL, pulmonary edema, and new headache or visual disturbances.
The amount of proteinuria and edema are not severe features.
HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) presents with nausea, malaise and right upper quadrant pain, sometimes with only mildly raised blood pressure.
Severe-range pressure that persists 15 minutes is treated within 30 to 60 minutes with IV labetalol, IV hydralazine or oral immediate-release nifedipine; labetalol is avoided in asthma, heart block and bradycardia.
Magnesium toxicity: loss of deep tendon reflexes first, then respiratory depression, decreased level of consciousness and cardiac arrest.
Magnesium is excreted by the kidneys, so oliguria causes accumulation.
Low-dose aspirin, started at 12 to 28 weeks and continued until birth, lowers the risk for high-risk clients.

Priority nursing actions

Give the prescribed antihypertensive for confirmed severe-range blood pressure and recheck every 10 to 20 minutes.
Start magnesium sulfate by infusion pump on a secondary line, with calcium gluconate at the bedside.
Assess blood pressure, respiratory rate, SpO2, deep tendon reflexes, level of consciousness, lung sounds and hourly urine output; monitor the fetal heart rate continuously.
For absent reflexes, respiratory rate below 12/min or urine output below 30 mL/hour, stop the infusion, notify the provider and give calcium gluconate as prescribed.
Keep seizure precautions: quiet, dim room, padded side rails, suction and oxygen ready.
During a seizure, turn the client to her side, protect her from injury, and time the seizure; afterward assess the fetus and watch for abruption.

Numbers to know

Value	Threshold or target	Why it matters
Blood pressure	140/90 mm Hg or higher twice, 4 hours apart, after 20 weeks	Defines gestational hypertension and preeclampsia
Severe range	160 systolic or 110 diastolic or higher	Treat within 30 to 60 minutes to prevent stroke
Platelets	Below 100,000/mm3 (100 x 10^9/L)	Severe feature and part of HELLP
Magnesium dosing	Loading 4 to 6 g IV over 20 to 30 minutes; then 1 to 2 g/hour	Continue 24 hours after birth
Therapeutic magnesium	4 to 7 mEq/L (2 to 3.5 mmol/L)	Higher levels cause toxicity
Respiratory rate	Below 12/min	Stop magnesium and report
Urine output	Below 30 mL/hour	Magnesium accumulates
Calcium gluconate	1 g (10 mL of 10% solution) IV slowly	Antidote for magnesium toxicity

Common exam traps

Choosing magnesium sulfate to lower the blood pressure: wrong because it prevents seizures; a separate antihypertensive is still needed.
Choosing 3+ proteinuria or ankle edema as a severe feature: wrong because neither defines severe disease.
Choosing IV labetalol for a client with asthma: wrong because a beta blocker can cause bronchospasm; question it.
Choosing to continue magnesium when reflexes are absent: wrong because loss of reflexes is the first sign of toxicity.
Choosing reassurance for right upper quadrant pain, nausea and low platelets with a nonsevere blood pressure: wrong because these findings suggest HELLP.

What to teach

Report severe headache, blurred vision or flashing lights, right upper quadrant or epigastric pain, sudden swelling of the face or hands, and shortness of breath.
Check and record blood pressure at home, count fetal movements daily, and keep every visit.
Magnesium causes flushing, warmth and drowsiness; report trouble breathing at once.
Preeclampsia can develop up to 6 weeks after birth; report these symptoms after discharge too.

Client handout: Preeclampsia: Know the Warning Signs (nurse guide and printable patient handout).

Try 2 NCLEX-style questions on this topic

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Question 1 · QID FF810235

A client at 34 weeks of gestation has a blood pressure of 152/98 mm Hg and 2+ proteinuria and is being evaluated for preeclampsia. For each additional finding, indicate whether it indicates preeclampsia with severe features or does not by itself indicate severe features.

For each finding, indicate whether it indicates preeclampsia with severe features or does not by itself indicate severe features.

	Indicates severe features	Does not by itself indicate severe features
Persistent headache with flashing lights unrelieved by acetaminophen
Platelet count of 85,000/mm3
Mild bilateral ankle edema at the end of the day
Urine protein of 3+ on dipstick
Blood pressure of 164/112 mm Hg on two readings 4 hours apart

Question 2 · QID 7AB0C1B5

A client at 33 weeks of gestation with preeclampsia has a blood pressure of 168/114 mm Hg that persists on recheck 15 minutes later. Her history includes moderate persistent asthma treated with an inhaled corticosteroid. The provider prescribes labetalol 20 mg intravenously. Which action should the nurse take?

Select the best answer.

A. Administer the prescribed IV labetalol immediately because rapid blood pressure reduction takes priority over the possibility of worsening the client's asthma
B. Hold the labetalol and substitute extended-release nifedipine by mouth using the standard hypertension dose while notifying the provider afterward
C. Question the prescription because labetalol can precipitate bronchospasm in a client with asthma
D. Start the magnesium sulfate infusion first and delay antihypertensive medication for 1 hour so seizure prevention is established before lowering the blood pressure

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More tips on Maternal & Newborn

Prenatal Care: Labs, Fundal Height and Danger SignsDate the pregnancy, time the routine prenatal labs, interpret fundal height, and teach the danger signs a pregnant client reports at once.Fetal Heart Rate Patterns and DecelerationsRead baseline, variability and decelerations, match each deceleration to its cause, and give intrauterine resuscitation in the right order.Postpartum Hemorrhage: Recognize Early, Act FastSpot hemorrhage before the blood pressure falls, firm a boggy uterus, empty the bladder, and give uterotonics within their contraindications.

Sources

American College of Obstetricians and Gynecologists. Practice Bulletin No. 222: Gestational Hypertension and Preeclampsia. Obstet Gynecol. 2020;135(6):e237-e260.
American College of Obstetricians and Gynecologists. Committee Opinion No. 767: Emergent Therapy for Acute-Onset, Severe Hypertension During Pregnancy and the Postpartum Period. Obstet Gynecol. 2019;133(2):e174-e180.
US Preventive Services Task Force. Aspirin Use to Prevent Preeclampsia and Related Morbidity and Mortality: US Preventive Services Task Force Recommendation Statement. JAMA. 2021;326(12):1186-1191.

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