A 28-year-old woman at 26 weeks of gestation is diagnosed with severe early-onset IUGR (estimated fetal weight <5th percentile) with absent end-diastolic velocity (AEDV) on umbilical artery Doppler. She is admitted for close fetal monitoring. Which agent should be administered to optimize fetal neuroprotection and reduce the risk of adverse neurological outcomes if preterm delivery becomes necessary?