A 24-year-old multiparous woman at 29 weeks of gestation is admitted with signs of preterm labor. Nifedipine tocolysis is initiated. Which agent should be administered concurrently for fetal neuroprotection?

Explanation

## Fetal Neuroprotection in Preterm Labor **Key Point:** Magnesium sulfate is the agent of choice for fetal neuroprotection in preterm labor <32 weeks of gestation, reducing the risk of cerebral palsy and intraventricular hemorrhage. ### Mechanism of Neuroprotection Magnesium sulfate acts as: - An NMDA (N-methyl-D-aspartate) receptor antagonist - A membrane stabilizer that reduces excitotoxicity - A vasodilator that improves cerebral blood flow - An anti-inflammatory agent **High-Yield:** Magnesium sulfate for neuroprotection is administered as a **loading dose of 6 g IV over 20–30 minutes**, followed by a **maintenance infusion of 2 g/hour until delivery or for 12 hours**, whichever comes first. ### Indications and Timing - **Gestational age:** 24–32 weeks (most evidence for <32 weeks) - **Timing:** Should be given as soon as preterm labor is diagnosed - **Efficacy:** Reduces cerebral palsy risk by approximately 30% in preterm neonates - **Number needed to treat (NNT):** ~46 to prevent one case of cerebral palsy **Clinical Pearl:** Magnesium sulfate is given **in addition to** nifedipine (or other tocolytic) and **in addition to** corticosteroids (betamethasone or dexamethasone). All three agents serve different roles and are complementary. ### Distinction: Tocolysis vs. Neuroprotection | Purpose | Agent | Mechanism | Duration | |---------|-------|-----------|----------| | **Tocolysis** (delay delivery) | Nifedipine | Calcium channel blocker | Until contractions stop or delivery | | **Neuroprotection** | Magnesium sulfate | NMDA antagonist | 12 hours or until delivery | | **Fetal lung maturity** | Betamethasone/Dexamethasone | Glucocorticoid | Single course (2 doses) | **Warning:** Magnesium sulfate is **NOT** a tocolytic agent — it does not reliably inhibit uterine contractions. It must be paired with a true tocolytic (nifedipine, indomethacin, or terbutaline). **Mnemonic:** **MgSO₄ = Neuro** (neuroprotection, not tocolysis). Remember: magnesium protects the fetal brain, not the uterus. [cite:ACOG Practice Bulletin 127; Cunningham OB 26e Ch 42; Mercer et al., NEJM 2008]