Inclusion Criteria:
1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study procedures and availability (meets psychosocial criteria below) for the duration of the study
3. Pregnant women, age 18 years and older
4. Singleton pregnancy
5. No pathogenic variants on microarray or pathologic findings on karyotype; results by fluorescence in situ hybridization (FISH) will be acceptable if patient is \>26 weeks
6. Fetal echocardiogram with changes expected with CDH and no major structural cardiac defects
7. Fetal CDH (left or right) with severe pulmonary hypoplasia, defined as o/e LHR \<25% with liver up
8. Gestational age at FETO procedure: if o/e LHR \<25%, will be done at 27 weeks plus 0 days to 29 weeks plus 6 days
9. Meets psychosocial criteria
* Willing to reside within 30 minutes of NewYork-Presbyterian Sloane Hospital for Women/Columbia University Irving Medical Center (CUIMC) and ability to maintain follow up appointments. NYP/CUIMC will work with the study participant to assist in securing housing 30 minutes from the hospital if this is a challenge to her.
* Patient has a support person (e.g. spouse, partner, friend, parent) that is available to stay with her for the duration of the pregnancy near NewYork-Presbyterian Sloane Hospital for Women/Columbia University Irving Medical Center (CUIMC)
* Willing to comply with restrictions of daily living including inability to exercise, have intercourse, or return to work
Exclusion Criteria:
1. Multi-fetal pregnancy
2. History of latex allergy
3. History of preterm labor or incompetent cervix (requiring cerclage), short cervix (\<20mm), or uterine anomaly predisposing to preterm labor
4. Psychosocial ineligibility
* Inability to reside within 30 minutes of NewYork-Presbyterian Sloane Hospital for Women/Columbia University Irving Medical Center (CUIMC) or inability to maintain follow up appointments
* Social work will meet with each patient to evaluate the social situation and support system. Identifiable issues of social instability or compliance with the protocol will exclude her as a potential candidate.
5. Bilateral CDH, unilateral CDH with o/e LHR \> 25%, or unilateral CDH with o/e LHR \<25% but liver completely down in abdomen
6. Additional fetal or genetic abnormalities that would impact care after delivery or be known to have an impact on outcome
7. Maternal contraindications to elective fetoscopic surgery
8. Significant placental abnormalities (abruption, chorioangioma, accreta) known at time of enrollment and/or surgery
9. Maternal-fetal Rh 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
10. No safe or feasible fetoscopic approach to balloon placement
11. Uterine anomaly such as large or multiple fibroids or mullerian duct abnormality
12. Participation in another intervention study that influences maternal and fetal morbidity and mortality.
