Trial of FETO for Severe Congenital Diaphragmatic Hernia

Inclusion Criteria: * Provision of signed and dated informed consent form * Pregnant individuals age 18 years and older * Singleton pregnancy * No pathogenic variants on prenatal chromosomal microarray or pathologic findings on karyotype analysis. Results by fluorescence in situ hybridization (FISH) will be acceptable if the patient is \> 26 weeks * Isolated left CDH with severe pulmonary hypoplasia with o/e LHR \</=25% with liver up (measured at 18 weeks 0 days to 29 weeks 5 days of gestation) OR Isolated right CDH with severe pulmonary hypoplasia with o/e LHR \</=35% with liver up (measured at 18 weeks 0 days to 29 weeks 5 days of gestation) * Gestational age at FETO procedure 27 weeks 0 days to 29 weeks 6 days as determined by clinical information and evaluation of first ultrasound * Fetal echocardiogram with changes expected with CDH and no major structural cardiac defects * Stated willingness to comply with all study procedures and lifestyle considerations and availability for the duration of the study * Willingness to reside within 30 minutes of the Chicago Institute for Fetal Health (CIFH) in the time period between the FETO placement procedure and the balloon retrieval procedure and ability to maintain follow up appointments * Subject has a support person (e.g., spouse, partner, friend, parent) that is available to stay with her for the duration of the pregnancy near Lurie Children's * Willingness to comply with study restrictions on work, exercise, and intercourse * Meets psychosocial criteria Exclusion Criteria: * Rubber latex allergy * Presence of chromosomal abnormalities or anatomic anomalies that are known to significantly alter survival prognosis (i.e., CDH and congenital heart disease). No cases will be removed post hoc if abnormalities are discovered during post-operative monitoring * History of preterm labor, cervix shortened to ≤20 mm at enrollment or at 24 hours prior to FETO balloon insertion procedure) or uterine anomaly strongly predisposing to preterm labor or placenta previa * Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy * History of incompetent cervix with or without cerclage * Placental abnormalities (previa, abruption, accreta, chorioangioma) known at time of enrollment * Maternal-fetal Rh isoimmunization, Kell sensitization or neonatal alloimmune thrombocytopenia affecting the current pregnancy * Maternal HIV, Hepatitis-B, Hepatitis-C status positive because of the increased risk of transmission to the fetus during maternal-fetal surgery. If the patient's HIV or Hepatitis status is unknown, the patient must be tested and found to have negative results before enrollment * Uterine anomaly such as large or multiple fibroids or mullerian duct abnormality * There is no safe or technically feasible fetoscopic approach to balloon placement * Participation in another intervention study that influences maternal and fetal morbidity and mortality * Any other condition which, in the opinion of the investigator, would compromise safety, feasibility or impede compliance