The primary purpose of administering intravenous magnesium sulfate in preterm labor is to:

• A. Delay delivery
• B. Prevent membrane rupture
• C. Enhance fetal lung maturity
• D. Stop the premature uterine contractions

Answer: (D)

Magnesium sulfate is used as a tocolytic to stop premature contractions by relaxing uterine smooth muscle. It works by reducing calcium availability in the myometrium and dampening nerve excitability, which lowers uterine contractions. The main goal in preterm labor is to halt contractions so birth can be delayed enough to give interventions that improve fetal outcomes, such as uterine relaxation and time for corticosteroids to help fetal lung maturity. It does not prevent the membranes from rupturing, and while briefly delaying birth can occur as contractions stop, the direct purpose is to stop the premature contractions. Monitor for signs of magnesium toxicity (decreased reflexes, respiratory depression, reduced urine output) and have calcium gluconate available as an antidote if needed.