What are the guidelines for intravenous magnesium sulfate (MgSO4) administration for neuroprotection in preterm pregnancy?

Guidelines for Intravenous Magnesium Sulfate for Neuroprotection in Preterm Pregnancy

Magnesium sulfate should be administered for fetal neuroprotection when preterm delivery is anticipated before 32 weeks' gestation, as it significantly reduces the risk of cerebral palsy without increasing mortality. 1

Indications and Timing

• Magnesium sulfate is recommended for fetal neuroprotection when delivery is anticipated before 32 weeks' gestation 1
• Administration should begin when preterm birth is imminent or planned within 24 hours 2
• Although data specific to the periviable period (22-25 weeks) are limited, magnesium sulfate prophylaxis is still recommended if delivery of a potentially viable infant is anticipated 1
• For maximum benefit, administration should occur within 12 hours of delivery 3

Dosing Regimen

• Standard loading dose: 4g intravenously over 20-30 minutes 4
• Maintenance dose: 1g/hour continuous infusion 4
• Duration: Continue for at least 4 hours and up to 24 hours, or until delivery occurs 4
• Alternative regimen used in some trials: 6g loading dose followed by 2g/hour maintenance 4
• The 50% magnesium sulfate solution must be diluted to 20% or less prior to IV infusion 5

Monitoring Requirements

• Maternal monitoring should include:
  • Patellar reflexes before each dose (if absent, no additional magnesium should be given until they return) 5
  • Respiratory rate (should remain ≥16 breaths/minute) 5
  • Blood pressure monitoring 5
  • Serum magnesium levels if available (therapeutic range: 2.5-5 mEq/L) 5
• Fetal monitoring should be considered if intrauterine resuscitation might affect newborn outcomes 1

Contraindications and Precautions

• Use with extreme caution in patients with:
  • Renal insufficiency (maximum dosage: 20g/48 hours with frequent monitoring of serum magnesium) 5
  • Myasthenia gravis 5
  • Digitalized patients (risk of heart block if calcium administration becomes necessary) 5
• Avoid continuous administration beyond 5-7 days due to risk of fetal bone abnormalities 5
• Injectable calcium salt should be immediately available to counteract potential magnesium toxicity 5

Clinical Efficacy

• Magnesium sulfate for neuroprotection has been shown to:
  • Reduce the incidence of cerebral palsy (RR 0.71,95% CI 0.57-0.89) 2
  • Reduce death or cerebral palsy combined (RR 0.87,95% CI 0.77-0.98) 2
  • Reduce substantial gross motor dysfunction (RR 0.60,95% CI 0.43-0.83) 6
  • Probably reduce severe intraventricular hemorrhage (RR 0.76,95% CI 0.60-0.98) 2

Potential Side Effects

• Maternal side effects may include:
  • Flushing, sweating, nausea, vomiting, headache, and injection site pain 5
  • More severe effects requiring discontinuation of treatment (RR 3.21,95% CI 1.88-5.48) 2
• Neonatal effects may include:
  • Transient hypotonia or respiratory depression if administered shortly before delivery 5
  • No increase in neonatal mortality has been observed 2

Concurrent Therapies

• Antenatal corticosteroids should be administered between 24+0 and 34+0 weeks of gestation when preterm delivery is anticipated 1
• In cases of fetal growth restriction with absent end-diastolic flow, delivery should be considered by 34 weeks gestation 1
• In cases of reversed end-diastolic flow, delivery should be considered by 30 weeks gestation 1

Special Considerations

• Magnesium sulfate may interact with CNS depressants, neuromuscular blocking agents, and cardiac glycosides 5
• For women with preeclampsia, magnesium sulfate serves dual purposes: prevention of eclamptic seizures and fetal neuroprotection 1
• The neuroprotective effect appears most significant for infants born at earlier gestational ages 4

Magnesium sulfate for fetal neuroprotection represents an important intervention to reduce the burden of cerebral palsy in preterm infants. While there are some maternal side effects, the benefits clearly outweigh the risks when used appropriately in the setting of anticipated preterm birth before 32 weeks' gestation.