Fetal Endoscopic Tracheal Occlusion for Congenital Diaphragmatic Hernia

Inclusion Criteria: * Singleton pregnancy * Normal fetal karyotype or microarray. Results by fluorescence in situ hybridization (FISH) will be acceptable if the patient is \> 26 weeks * Isolated severe left CDH with O/E LHR \< 25% ) * Gestation age at enrollment prior to 29 wks plus 6 days. * Pulmonary hypoplasia with ultrasound O/E LHR \< 25% (measured at 18 0/7 to 29 5/7 weeks) at the time of surgery. * Gestational age at FETO procedure 27 weeks 0 days to 29 weeks 6 days as determined by clinical information (LMP) and evaluation of first ultrasound * Patient meets psychosocial criteria: able to reside within 30 minutes of Mayo Clinic, Rochester and able to comply with the travel for the follow-up requirements of the trial; patient has a support person (e.g. spouse, partner, mother) available to stay with the patient for the duration of the pregnancy at Mayo Clinic * Patient is willing and able to give informed consent * Appropriate multi-disciplinary counseling performed with maternal-fetal medicine, neonatology, pediatric surgery, genetics, pediatric otolaryngology (ENT) Exclusion Criteria: * Multi-fetal pregnancy * History of natural rubber latex allergy * Preterm labor, cervix shortened (\<20 mm) at enrollment or within 24 hours of FETO balloon insertion procedure) or uterine anomaly strongly predisposing to preterm labor * Psychosocial ineligibility, precluding consent: inability to reside within 30 minutes of Mayo Clinic, Rochester and inability to comply with the travel for the follow-up requirements of the trial; patient does not have a support person (e.g. spouse, partner, mother) available to stay with the patient for the duration of the pregnancy at Mayo Clinic * Right sided CDH or bilateral CDH, isolated left sided with O/E LHR \>25% measured at 18 0/7 to 29 6/7 weeks) as determined by ultrasound * Additional fetal anomaly and chromosomal abnormalities by ultrasound, MRI, or echocardiogram that will significantly worsen prognosis. No cases will be removed post hoc if abnormalities are discovered in the course of post-operative monitoring * Maternal contraindication to fetoscopic surgery * History of incompetent cervix with or without cerclage * Placental abnormalities (previa, abruption, accreta) 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. * Uterine anomaly such as large or multiple fibroids or mullerian duct abnormality that will make the procedure technically unfeasible * No safe or technically feasible fetoscopic approach to balloon placement * Participation in another intervention study that influences maternal and fetal morbidity and mortality or participation in this trial in a previous pregnancy