Fetal Endotracheal Occlusion (FETO) in Fetuses With Severe Congenital Diaphragmatic Hernia

Inclusion Criteria: * Pregnant patient 18 and older who is able to consent * Singleton pregnancy * Ability to reside within 30 minutes of Boston Children's Hospital for the duration of the FETO intervention, from the time of balloon placement until balloon removal * Patient has a support person who is able to stay with them for the duration of the pregnancy Fetal: * Reassuring genetic analysis demonstrated by either normal Karyotype, normal fluorescence in situ hybridization (FISH) for chromosomes 13, 18, 21, X and Y, or chromosomal microarray (CMA) with non-pathologic variants * Diagnosis of isolated left CDH with liver up * Gestation at enrollment prior to 29 weeks 5 days * SEVERE pulmonary hypoplasia with ultrasound Observed/Expected Lung-to-Head Ratio (O/E LHR) \< 25% Exclusion Criteria: * Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy * Technical limitations precluding fetoscopic surgery, including uterine anomaly such as large or multiple fibroids, or Mullerian duct anomaly * Latex allergy * Preterm labor, shortened cervix (\<20mm at enrollment or within 24 hours of FETO balloon insertion procedure) or uterine anomaly strongly predisposing to preterm labor, placenta previa * Severe maternal obesity pre-pregnancy (BMI \> 40) * Psychosocial ineligibility, precluding consent, as determined by clinic social worker during review * Inability to remain at FETO site during time period of tracheal occlusion, delivery, and p…