Prenatal Ultrasound and MRI of Bowel Abnormalities in Cystic Fibrosis with In Utero CFTR Modulator Exposure: A Case Series.

INTRODUCTION: Cystic fibrosis (CF) can present prenatally as fetal hyperechogenic bowel (FEB) or meconium ileus (MI), indicating early CFTR dysfunction. Elexacaftor/tezacaftor/ivacaftor (ETI) partially restores CFTR function and limited reports suggest it may benefit fetuses when administered maternally. CASE PRESENTATION: We report four pregnancies in CF carrier mothers with confirmed or presumed fetal CF after FEB detection, treated off-label with ETI. Fetal bowel status was monitored via ultrasound and MRI, and maternal safety was assessed. In Case 1, ETI from 26-36 weeks normalized bowel appearance; the infant had normal meconium passage. In Case 2, ETI at 30 weeks improved bowel findings in a fetus with CF and congenital diaphragmatic hernia, but the neonate died from hernia complications. Case 3 involved a single ETI dose before preterm birth at 28 weeks; the infant had severe MI and died from neurological complications. In Case 4, ETI at 35 weeks briefly improved bowel status; delivery at 37 weeks was required for progressive distension, followed by MI surgery with full recovery. Maternal therapy was well tolerated. CONCLUSIONS: Prenatal ETI may improve fetal bowel abnormalities and reduce MI risk, particularly with early, sustained exposure. Imaging effectively monitored response. Further studies are required to define optimal timing, protocols, and long-term safety.