• 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 or right 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)

• 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