Inclusion Criteria:

• * Singleton pregnancy
• * Normal fetal karyotype with confirmation by culture results. Results by fluorescence in situ hybridization (FISH) will be acceptable if the patient is \> 26 weeks.
• * Isolated Left CDH with liver up
• * Gestation age at enrollment prior to 29 wks plus 6 days severe pulmonary hypoplasia with ultrasound (US) O/E lung area to head circumference ratio (LHR) \< 25% (measured at 180 to 296 weeks) at the time of surgery; O/E LHR 25% to \<30% (measured at 300 to 316 weeks) at time of surgery.
• * Gestational age at FETO procedure with O/E LHR \<25% at 27 weeks 0 days to 29 weeks 6 days; with O/E LHR 25% to \<30% at 30 weeks 0 days to 31 weeks 6 days as determined by clinical information (LMP) and evaluation of first ultrasound
• * Patient meets psychosocial criteria

Exclusion Criteria:

• * Multi-fetal pregnancy
• * History of natural rubber latex allergy
• * Preterm labor, cervix shortened (\<15 mm at enrollment or within 24 hours of FETO balloon insertion procedure) or uterine anomaly strongly predisposing to preterm labor, placenta previa
• * Psychosocial ineligibility, precluding consent:
• * Inability to reside within 30 minute drive of our hospital, 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 our institution.
• * Right sided CDH or bilateral CDH, isolated left sided with O/E LHR ≥30% (measured at 180 to 295 weeks) as determined by ultrasound
• * Additional fetal anomaly and chromosomal abnormalities by ultrasound, MRI, or echocardiogram at the fetal treatment center. No cases will be removed post hoc if abnormalities are discovered in the course of postoperative monitoring
• * Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy
• * History of incompetent cervix with or without cerclage
• * Placental abnormalities (previa, abruption, accrete) 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 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 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 or participation in this trial in a previous pregnancy