The purpose of the study is to study the efficacy of fetal endoscopic tracheal occlusion (FETO) in cases of severe congenital diaphragmatic hernia (CDH). This study will also collect safety and effectiveness data for the off-label use of the FETO Goldballoon (the balloon that will be inserted into the fetal trachea), manufactured by Balt medical. The investigators hope to study the risks and benefits of FETO in cases of severe CDH in an advanced medical center such as Lucile Packard Children's Hospital (LPCH) Stanford with access to advanced maternal-fetal medicine, neonatal services, and neonatal ECMO, and pediatric surgery.

Inclusion Criteria:

• Maternal Age: 18-50
• Singleton gestation
• Gestational age before 29 weeks 6 days
• Severe left or right-sided CDH: For severe left sided CDH observed-to-expected lung-to- head ratio (o/e LHR) less than 25% between 22 and 29 6/7 weeks' gestation, liver herniation, MRI lung volumes less than 30% expected based on gestational age nomograms. For severe right sided CDH o/e LHR less than 30 % between 22 and 29 6/7 weeks' gestation, liver herniation, MRI lung volumes less than 30% expected based on gestational age nomograms.
• Normal genetic karyotype or microarray testing by amniocentesis or chorionic villus sampling (CVS)
• Absence of associated fetal structural cardiac anomalies by a dedicated fetal echocardiogram
• Absence of other structural anomalies by ultrasound or MRI
• Appropriate multi-disciplinary counseling performed with maternal-fetal medicine, neonatology, pediatric surgery, genetics, pediatric otolaryngology (ENT).
• Must be willing to remain near LPCH Stanford (within 30 minutes from the hospital) for the duration of the balloon placement.
• No maternal and/or fetal contra-indications to fetal surgery such as a bleeding disorder, poorly controlled diabetes or hypertension, short cervix (measuring < 20mm), risk for preterm birth etc.
• Planned pregnancy surveillance at LPCH Stanford
• Planned delivery at LPCH Stanford
• Able to provide written consent
• Willingness to comply with all study procedures and availability (meets psychosocial criteria) for the duration of the study including having a support person

Exclusion Criteria:

• Contraindications to fetal surgery including poorly controlled hypertension, diabetes or other maternal medical condition including hematological disorder
• High risk for preterm labor and/or delivery based on either significant history of preterm birth, short cervix (measuring < 20mm), significant uterine anomaly or other risk factor, incompetent cervix (requiring cerclage)
• Non-isolated CDH - CDH with additional structural anomalies
• Significant maternal obesity defined as a body mass index (BMI) greater than 40. BMI is a calculation which includes a person's height and weight
• History of natural rubber latex allergy
• Uterine anomaly such as large or multiple fibroids or mullerian duct abnormality
• Participation in another intervention study that influences maternal and fetal morbidity and mortality.
• Bilateral CDH, left-sided CDH with O/E LHR >25%, or left-sided CDH with O/E LHR <25% but liver completely down in abdomen
• Right-sided CDH O/E LHR >30% or right-sided CDH with O/E LHR <30% with liver completely down in abdomen
• Significant placental abnormalities (abruption, chorioangioma, accreta) known at the time of enrollment and/or surgery
• Maternal-fetal Rhesus isoimmunization, Kell sensitization or neonatal alloimmune thrombocytopenia, affecting the current pregnancy.
• Maternal HIV, Hepatitis B with positive surface antigen, Hepatitis C with presence of virus in maternal blood due to risk of fetal transmission during the procedure
• No safe or feasible fetoscopic approach to balloon placement.