Intravenous magnesium sulfate 4 g loading dose over 15 to 20 minutes, followed by an infusion of 1 g/hour. This patient has suffered an eclamptic convulsion in the setting of severe pre-eclampsia. Under Australian guidelines (SOMANZ) and international consensus, intravenous magnesium sulfate is the anticonvulsant of choice for the prevention and treatment of eclamptic seizures, proven superior to diazepam, phenytoin, or lytic cocktails. The standard regimen consists of an intravenous loading dose of 4 g of magnesium sulfate diluted in 0.9% sodium chloride infused over 15 to 20 minutes, followed by a continuous maintenance infusion of 1 g/hour for at least 24 hours postpartum or after the last convulsion. Benzodiazepines and phenytoin are less effective in terminating eclamptic seizures, increase maternal and neonatal respiratory depression, and are reserved only as third-line agents when magnesium sulfate is strictly contraindicated (e.g., in myasthenia gravis). Urgent antihypertensive therapy (e.g., intravenous labetalol or hydralazine) is also mandatory, and delivery is the definitive resolution once the mother is stabilized.

Q: A 34-year-old woman with severe pre-eclampsia at 32 weeks gestation is receiving a continuous intravenous maintenance infusion of magnesium sulfate at 1 g/hour following an eclamptic seizure. Two hours into the infusion, nursing observations document a blood pressure of 142/88 mmHg, a heart rate of 82 beats per minute, a respiratory rate of 8 breaths per minute, and a urine output of 45 mL over the past hour. Neurological examination reveals that her deep tendon (patellar) reflexes, which were brisk with clonus at baseline, are now completely absent bilaterally. Which of the following is the most appropriate immediate action?

Cease the magnesium sulfate infusion immediately and administer intravenous 10% calcium gluconate 10 mL. Magnesium sulfate toxicity follows a well-established physiological progression directly correlated with serum magnesium concentrations. Loss of deep tendon (patellar) reflexes is the earliest clinical manifestation of hypermagnesaemia, typically appearing at serum levels between 3.5 and 5.0 mmol/L (therapeutic range is 2.0 to 3.5 mmol/L). If unaddressed, toxicity progresses rapidly to respiratory depression (respiratory rate < 12 breaths/min) at 5.0 to 6.5 mmol/L, altered consciousness, and cardiac arrest at levels exceeding 7.5 mmol/L. When deep tendon reflexes are lost, the magnesium sulfate infusion must be ceased immediately, and the specific antidote, 10% calcium gluconate (10 mL infused intravenously over 3 to 5 minutes), should be administered to antagonize the membrane and neuromuscular actions of magnesium. Diuretics and fluid overloading are hazardous in pre-eclampsia due to contracted intravascular volume and high susceptibility to pulmonary oedema.

Q: A 33-year-old multipara at 32 weeks gestation presents to the emergency department after waking in a pool of bright red vaginal blood. She denies any abdominal pain, uterine contractions, or antecedent trauma. On physical examination, her vital signs are stable with a blood pressure of 116/72 mmHg and a heart rate of 78 beats per minute. Abdominal examination reveals a soft, non-tender, non-distended uterus consistent with 32 weeks gestational size. The fetus is in a high, transverse lie, and the fetal heart rate is 140 beats per minute with normal variability on cardiotocography. Which of the following is strictly contraindicated in the initial assessment of this patient?

Performing a digital vaginal examination to assess cervical effacement and dilatation status. This patient's presentation of painless, bright red antepartum haemorrhage accompanied by a soft, non-tender uterus and an abnormal fetal lie (transverse lie) is classic for placenta praevia. In all women presenting with antepartum haemorrhage, digital vaginal examination is strictly contraindicated until placenta praevia has been definitively excluded by ultrasound imaging. Digital palpation of the cervix in the presence of placenta praevia can cause mechanical disruption of the low-lying placental attachment or cervical sinusoids, precipitating catastrophic and potentially exsanguinating maternal haemorrhage. Transabdominal and transvaginal ultrasonography are safe and highly accurate diagnostic modalities. Initial care mandates large-bore intravenous access, crossmatching of packed red cells, administration of anti-D immunoglobulin if the patient is Rh(D)-negative, and administration of antenatal corticosteroids (betamethasone) to reduce neonatal morbidity associated with preterm birth.

Key Takeaways

Magnesium sulfate treats eclampsia and requires toxicity monitoring.
Stop magnesium and seek urgent treatment if toxicity develops.
Placental abruption severity is not reliably measured by visible vaginal blood loss.

Last updated: October 2026

Eclampsia and Seizure Management

Eclampsia is defined as the occurrence of generalized tonic-clonic convulsions in a woman with pre-eclampsia, which cannot be attributed to other neurological pathology (e.g., epilepsy, intracranial haemorrhage, encephalitis).

Emergency Resuscitation and Anticonvulsant Protocol

During an eclamptic seizure: Protect from injury, position safely, call for help and support oxygenation/airway as needed. Never insert a bite guard, fingers or any object into the mouth. Give magnesium under the emergency protocol and treat severe blood pressure.

First-Line Anticonvulsant — Magnesium Sulfate ( $MgSO_4$ ):
- Loading Dose: $4\text{ g}$ IV diluted in 0.9% sodium chloride, infused slowly over 15 to 20 minutes.
- Maintenance Infusion: Continuous intravenous infusion of $1\text{ g/hour}$ for at least 24 hours following delivery or the last seizure.
- Recurrent Seizure during Infusion: Administer an additional IV bolus of $2\text{ g}$ $MgSO_4$ over 5 minutes.
Clinical Monitoring for Magnesium Toxicity:
- Patellar (Deep Tendon) Reflexes: Checked hourly; must remain present.
- Respiratory Rate: Checked hourly; must remain $\ge 12\text{ breaths/min}$ .
- Urine Output: Measured hourly via indwelling Foley catheter; must exceed $\ge 25\text{–}30\text{ mL/hour}$ because magnesium is eliminated exclusively by the kidneys.
- Therapeutic Serum Magnesium Range: $2.0\text{ to }3.5\text{ mmol/L}$ .
- Toxicity Progression: Loss of patellar reflexes occurs at $3.5\text{–}5.0\text{ mmol/L}$ ; respiratory depression develops at $5.0\text{–}6.5\text{ mmol/L}$ ; and cardiac conduction blocks / asystole occur at $> 7.5\text{ mmol/L}$ .
- Magnesium Antidote: If toxicity is suspected (absent reflexes or respiratory rate $< 12$ ), cease the infusion immediately and administer intravenous calcium gluconate 10% ( $10\text{ mL}$ [1 g]) slowly over 3 to 5 minutes.

Abruption: Stabilise the mother and assess fetal status, bleeding and coagulopathy. Delivery route depends on urgency, fetal compromise and whether vaginal birth is imminent. Not every abruption with a live fetus requires immediate caesarean delivery. Normal ultrasound does not exclude abruption.

HELLP Syndrome

HELLP syndrome is a severe variant of pre-eclampsia characterized by endothelial injury, microvascular thrombi, and hepatic sinusoid obstruction:

H (Haemolysis): Microangiopathic haemolytic anaemia demonstrated by fragmented red blood cells (schistocytes, burr cells) on blood film, elevated serum lactate dehydrogenase (LDH) $> 600\text{ U/L}$ , unconjugated hyperbilirubinaemia, and low serum haptoglobin.
EL (Elevated Liver Enzymes): Serum transaminases (ALT or AST $\ge 70\text{ U/L}$ or $> 2 \times$ upper limit of normal).
LP (Low Platelets): Thrombocytopenia with platelet count $< 100 \times 10^9\text{/L}$ .

Antepartum Haemorrhage (APH)

Antepartum haemorrhage is defined as genital tract bleeding occurring from $20^{+0}$ weeks gestation until the birth of the baby. The two most critical causes are placenta praevia and placental abruption.

Placenta Praevia

Placental location: Placenta praevia overlies the internal os; a placental edge within 20 mm but not covering it is low lying. Transvaginal ultrasound is safe and clarifies location. Avoid digital vaginal examination until praevia has been excluded.
Risk Factors: Previous caesarean section (risk escalates dramatically with each additional caesarean), multiparity, advanced maternal age, prior uterine curettage, multiple pregnancy, and smoking.
Clinical Presentation: Recurrent episodes of painless, bright red vaginal bleeding occurring spontaneously without provocative trauma or contractions. On abdominal examination, the uterus is soft, non-tender, and relaxed, and the fetal lie is frequently abnormal (transverse, oblique, or high floating breech). The fetal heart rate and cardiotocography (CTG) are typically normal and reassuring.
The Cardinal Rule: NEVER perform a digital vaginal examination in any woman presenting with antepartum haemorrhage until placenta praevia has been definitively excluded by ultrasound. Digital disruption of low-lying placental cotyledons or cervical vessels can provoke sudden, life-threatening exsanguination.
Diagnosis and Management: Transvaginal ultrasonography (TVS) is safe and superior to transabdominal scanning for assessing the relationship of the placental edge to the internal os. Management involves hospital admission, large-bore IV access, crossmatching 2 to 4 units of packed red blood cells, administration of anti-D if Rh-negative, and planned elective caesarean section at $36^{+0}\text{ to }37^{+6}$ weeks (or emergent delivery if massive unremitting haemorrhage ensues).

Placental Abruption (Abruptio Placentae)

Definition: Premature separation of a normally located placenta from the decidua basalis prior to delivery of the fetus.
Risk Factors: Maternal chronic hypertension or pre-eclampsia (strongest risk factor), blunt abdominal trauma (motor vehicle collision, domestic violence), illicit substance abuse (cocaine, amphetamines), cigarette smoking, sudden uterine decompression (rupture of membranes in polyhydramnios or delivery of first twin), and prior abruption.
Clinical Presentation: Painful, dark red vaginal bleeding accompanied by continuous, severe abdominal or lower back pain. On physical examination, the uterus is hypertonic, tense, rigid ("woody"), and exquisitely tender to palpation. Signs of maternal hypovolaemic shock (tachycardia, hypotension, pallor) are frequently out of proportion to visible vaginal blood loss because a substantial proportion of bleeding may be concealed retroplacentally (in ~20% of cases).
Fetal and Coagulation Status: Cardiotocography shows fetal compromise (repetitive late decelerations, prolonged deceleration, fetal bradycardia) or intrauterine fetal demise. Consumption of clotting factors by the large retroplacental clot frequently leads to disseminated intravascular coagulation (DIC), evidenced by hypofibrinogenaemia ( $< 2.0\text{ g/L}$ ), prolonged PT/APTT, and elevated D-dimer.

Clinical Comparison: Placenta Praevia vs. Placental Abruption

Vaginal Bleeding: Placenta Praevia: Painless, bright red, recurrent; visible bleeding matches clinical loss; Placental Abruption: Painful, dark red, continuous; may be concealed retroplacentally
Abdominal Pain: Placenta Praevia: Completely absent; Placental Abruption: Severe, constant abdominal and back pain
Uterine Palpation: Placenta Praevia: Soft, relaxed, non-tender, non-irritable; Placental Abruption: Tense, rigid, "woody", exquisitely tender with high resting tone
Fetal Presentation: Placenta Praevia: Commonly abnormal (transverse lie, oblique, high breech); Placental Abruption: Usually normal engagement matching gestational age
Cardiotocography (CTG): Placenta Praevia: Normal, reassuring fetal heart rate pattern; Placental Abruption: Pathological (late decelerations, severe bradycardia, or absent fetal heart)
Maternal Haemodynamics: Placenta Praevia: Proportional to visible external blood loss; Placental Abruption: Often in hypovolaemic shock out of proportion to visible loss
Coagulopathy (DIC): Placenta Praevia: Extremely rare; Placental Abruption: Common complication (hypofibrinogenaemia $< 2\text{ g/L}$ )
Digital Vaginal Exam: Placenta Praevia: Strictly contraindicated (provokes torrential haemorrhage); Placental Abruption: Strictly contraindicated until ultrasound excludes praevia
Initial Management: Placenta Praevia: TVS confirmation, crossmatch, anti-D, elective C-section; Placental Abruption: Emergent resuscitation, blood/cryoprecipitate, category 1 C-section

Primary references (checked 7 October 2026): Queensland maternity guidelines.

Test Your Knowledge

A 29-year-old primigravida at 35 weeks gestation presents to the maternity assessment unit with a severe frontal headache, blurred vision, and epigastric discomfort. Her blood pressure is 174/112 mmHg on repeated measurements. While an intravenous cannula is being inserted, she suddenly becomes unresponsive, demonstrates tonic-clonic motor activity lasting 75 seconds, and remains post-ictal. Vital signs following the seizure show a blood pressure of 168/108 mmHg, heart rate of 110 beats per minute, and oxygen saturation of 96% on room air. Cardiotocography shows a fetal baseline heart rate of 145 beats per minute with reduced variability. Which of the following is the most appropriate immediate medical pharmacotherapy to prevent recurrent convulsions?

Intravenous diazepam 10 mg administered as a slow push, followed by an oral levetiracetam maintenance regimen

Intravenous magnesium sulfate 4 g loading dose over 15 to 20 minutes, followed by an infusion of 1 g/hour

Intravenous phenytoin 1 g loading dose infused over one hour, followed by continuous cardiac telemetry monitoring

Intravenous midazolam 5 mg bolus, followed by urgent intubation and general anaesthetic induction in theatre

Test Your Knowledge

A 34-year-old woman with severe pre-eclampsia at 32 weeks gestation is receiving a continuous intravenous maintenance infusion of magnesium sulfate at 1 g/hour following an eclamptic seizure. Two hours into the infusion, nursing observations document a blood pressure of 142/88 mmHg, a heart rate of 82 beats per minute, a respiratory rate of 8 breaths per minute, and a urine output of 45 mL over the past hour. Neurological examination reveals that her deep tendon (patellar) reflexes, which were brisk with clonus at baseline, are now completely absent bilaterally. Which of the following is the most appropriate immediate action?

Continue the magnesium sulfate infusion at the current rate and recheck reflexes in two hours

Reduce the magnesium sulfate infusion to 0.5 g/hour and administer an intravenous furosemide 20 mg bolus

Cease the magnesium sulfate infusion immediately and administer intravenous 10% calcium gluconate 10 mL

Increase the intravenous fluid rate to 250 mL/hour to accelerate renal excretion of magnesium ions

Test Your Knowledge

A 33-year-old multipara at 32 weeks gestation presents to the emergency department after waking in a pool of bright red vaginal blood. She denies any abdominal pain, uterine contractions, or antecedent trauma. On physical examination, her vital signs are stable with a blood pressure of 116/72 mmHg and a heart rate of 78 beats per minute. Abdominal examination reveals a soft, non-tender, non-distended uterus consistent with 32 weeks gestational size. The fetus is in a high, transverse lie, and the fetal heart rate is 140 beats per minute with normal variability on cardiotocography. Which of the following is strictly contraindicated in the initial assessment of this patient?

Performing transabdominal ultrasonography to determine placental location and fetal biometry

Inserting two large-bore intravenous cannulae and sending blood for full blood count and crossmatch

Administering intramuscular betamethasone 11.4 mg to accelerate fetal pulmonary maturity

Performing a digital vaginal examination to assess cervical effacement and dilatation status

Sections you finish are checked off in the contents.

Up Next

Labour physiology and CTG assessment

Intrapartum Monitoring, Postpartum Haemorrhage & Obstetric Emergencies

Independent exam preparation notice

OpenExamPrep is an independent education provider, not affiliated with or endorsed by the exam sponsors named on this site. Exam and certification names identify what our resources help you study for; they do not imply sponsorship, approval, or review of our materials. Unless a resource expressly identifies authorized public material, our practice questions are independently developed simulations, not actual, recalled, or sponsor-provided exam items. We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.