Can a tiny balloon in the womb help babies breathe?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Provision of a signed and dated informed consent form 2. Pregnant individuals age 18 years and older 3. Singleton pregnancy 4. A normal karyotype with confirmation by culture results, CMA with non-pathologic variants, whole exome or genome sequencing (WES or WGS). 5. Isolated left CDH with severe pulmonary hypoplasia with o/e LHR less than 25% with liver up (measured at 18 weeks 0 days to 29 weeks 5 days of gestation) 6. Isolated right CDH with severe pulmonary hypoplasia with o/e LHR equal or less than 30% with liver up (measured at 18 weeks 0 days to 29 weeks 5 days of gestation) 7. 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 8. Stated willingness to comply with all study procedures and lifestyle considerations and availability for the duration of the study 9. Willing to reside within a 30-minute distance of the NYULH in the time period between the FETO placement procedure and the balloon retrieval procedure, and ability to maintain follow-up appointments 10. The subject has a support person (e.g., spouse, partner, friend, parent) who is available to stay with her for the duration of the pregnancy near NYULH. 11. Willing to comply with restrictions of daily living, including inability to exercise, have intercourse, or return to work 12. Meets psychosocial criteria Exclusion Criteria: 1. Natural rubber latex allergy 2. Additional fetal anomaly and chromosomal abnormalities, associated anomalies recognized to alter survival prognosis (i.e., congenital heart disease) or presence of an underlying genetic syndrome (i.e., Fryns) by ultrasound, MRI or echocardiogram at the fetal treatment center. 3. Signs of preterm labor, cervix shortened to ≤20 mm at enrollment or at 24 hours prior to FETO balloon insertion procedure) or a uterine anomaly strongly predisposing to preterm labor. 4. Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy 5. History of incompetent cervix with or without cerclage 6. Placental abnormalities (previa, abruption, accreta, chorioangioma) known at time of enrollment 7. Maternal-fetal Rh isoimmunization, Kell sensitization or neonatal alloimmune thrombocytopenia affecting the current pregnancy 8. 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 9. Uterine anomaly such as large or multiple fibroids or mullerian duct abnormality 10. There is no safe or technically feasible fetoscopic approach to balloon placement 11. Participation in another intervention study that influences maternal and fetal morbidity and mortality 12. Any other condition which, in the opinion of the investigator, would compromise safety, feasibility or impede compliance. 13. Bilateral CDH, isolated left sided CDH with o/e LHR \>/= 25% and isolated right sided CDH \>30% 14. No intrathoracic liver herniation