What is the recommended dosage and usage of magnesium (Mg) supplementation for pregnant women?

Magnesium Supplementation for Pregnant Women

Magnesium supplementation during pregnancy should be provided as 1.5-2 g of elemental calcium daily for women with low calcium intake (<800 mg/day) to reduce the risk of preeclampsia, and magnesium sulfate should be administered at 4-5g IV loading dose followed by 1-2g/hour maintenance for women with preeclampsia to prevent eclampsia. 1, 2

Routine Magnesium Supplementation

For General Pregnancy Health

• Pregnant women should be counseled to increase intake of magnesium-rich foods (nuts, seeds, beans, leafy greens) 3
• For women with low dietary magnesium intake, supplementation may be considered, though evidence for routine supplementation in all pregnant women is limited 3

For Women with Low Calcium Intake

• For pregnant women with low calcium intake (<800 mg/day):
  • Calcium replacement (<1 g elemental calcium/day) OR
  • Calcium supplementation (1.5-2 g elemental calcium/day)
  • This may reduce the burden of both early and late-onset preeclampsia 1

Magnesium Sulfate for Preeclampsia/Eclampsia

Indications

• Magnesium sulfate should be given to women with:
  • Preeclampsia with severe hypertension
  • Preeclampsia with neurological signs or symptoms
  • HELLP syndrome with co-existing severe hypertension 1
  • As a neuroprotective agent for preterm preeclampsia if delivery is required before 32 weeks' gestation 1

Dosage and Administration

• Loading dose: 4-5g IV magnesium sulfate in 250 mL of 5% Dextrose or 0.9% Sodium Chloride over 15-20 minutes 2, 4
• Maintenance dose: 1-2g/hour by constant IV infusion 2, 4
• Alternative regimen (when IV administration is not possible):
  • 4g IV loading dose followed by 10g IM (5g in each buttock)
  • Then 5g IM every 4 hours in alternating buttocks 5
• Duration: Continue for 24 hours postpartum 1, 2

Monitoring During Administration

• Monitor maternal reflexes continuously
• Restrict total fluid intake to 60-80 mL/hour during administration 2
• Monitor for signs of magnesium toxicity:
  • Loss of patellar reflex (first warning sign) at plasma concentrations of 3.5-5 mmol/L
  • Respiratory depression at 5-6.5 mmol/L
  • Cardiac conduction abnormalities at >7.5 mmol/L 5

Special Considerations

Efficacy and Safety

• Therapeutic plasma concentration for treatment of eclamptic convulsions: 1.8-3.0 mmol/L 5
• Magnesium sulfate reduces the risk of eclampsia by approximately half 1
• Continuous use of magnesium sulfate in pregnancy beyond 5-7 days can cause fetal abnormalities 4

Potential Side Effects

• Maternal: Flushing, nausea, headache, drowsiness, muscle weakness
• Neonatal: Hypotonia, lower Apgar scores, increased need for intubation in delivery room with increasing maternal serum magnesium concentrations 6

Important Caveats

• Despite the benefits of magnesium for preeclampsia prevention and treatment, routine oral magnesium supplementation has not been shown to reduce preeclampsia incidence in low-income, low-risk pregnant women 7
• Magnesium dosing should be reduced in women with renal insufficiency; maximum dosage is 20g/48 hours with frequent monitoring of serum magnesium concentrations 4
• Each healthcare facility should have clear clinical protocols for magnesium sulfate use, as this is a key education priority 1

By following these evidence-based recommendations for magnesium supplementation and treatment during pregnancy, clinicians can help reduce maternal and fetal morbidity and mortality associated with preeclampsia and eclampsia.