Magnesium sulfate in women at risk of preterm delivery

• a systemic review into the efficacy of antenatal magnesium sulphate and risk of cerebral palsy in preterm infants revealed (1):
  • antenatal magnesium sulfate therapy given to women at risk of preterm birth substantially reduced the risk of cerebral palsy in their children (relative risk [RR] 0.69; 95% confidence interval [CI] 0.54-0.87; five trials; 6,145 infants). The number needed to treat to prevent one case of cerebral palsy was 63 (95% CI 43-155)
  • there was a significant reduction in the rate of substantial gross motor dysfunction (RR 0.61; 95% CI 0.44-0.85; four trials; 5,980 infants)
  • no statistically significant effect of antenatal magnesium sulfate therapy was detected on pediatric mortality (RR 1.01; 95% CI 0.82-1.23; five trials; 6,145 infants), or on other neurologic impairments or disabilities in the first few years of life
  • no significant effects of antenatal magnesium sulfate on combined rates of mortality with neurologic outcomes, except in the studies where the primary intent was neuroprotection, where there was a reduction in death or cerebral palsy (RR 0.85; 95% CI 0.74-0.98; four trials; 4,446 infants)
  • study authors concluded that antenatal magnesium sulfate therapy given to women at risk of preterm birth is neuroprotective against motor disorders in childhood for the preterm fetus

NICE suggest (2):

• magnesium sulfate for neuroprotection
  • for women between 23+0 and 23+6 weeks of pregnancy who are in established preterm labour or having a planned preterm birth within 24 hours, discuss with the woman (and her family members or carers as appropriate) the use of intravenous magnesium sulfate[*] for neuroprotection of the baby, in the context of her individual circumstances
    
    
  • offer intravenous magnesium sulfate for neuroprotection of the baby to women between 24+0 and 29+6 weeks of pregnancy who are:
    • in established preterm labour or
    • having a planned preterm birth within 24 hour
      
      
  • consider intravenous magnesium sulfate[*] for neuroprotection of the baby for women between 30+0 and 33+6 weeks of pregnancy who are:
    • in established preterm labour or
    • having a planned preterm birth within 24 hours
      
      
• * although this use is common in UK clinical practice, at the time of publication (August 2019), magnesium sulfate did not have a UK marketing authorisation for this indication. The prescriber should see the SPC for the manufacturer's advice on use in pregnancy. The prescriber should follow relevant professional guidance, taking full responsibility for the decision. Informed consent should be obtained and documented. See the General Medical Council's Prescribing guidance: prescribing unlicensed medicines for further information

NHS England report that (3):

• for every 37 women receiving magnesium sulphate, one fewer baby will be affected by cerebral palsy

Reference:

• 1) Doyle LW, Crowther CA, Middleton P, Marret S. Antenatal magnesium sulfate and neurologic outcome in preterm infants: a systematic review. Obstet Gynecol. 2009 Jun;113(6):1327-33
• 2) NICE (August 2019).Preterm labour and birth
• 3) NHS England (June 20th 2023). PReCePT – using magnesium sulphate to reduce cerebral palsy in pre-term babies