The goal is to assess the feasibility and safety of implementing Fetoscopic Endoluminal Tracheal Occlusion (FETO) therapy in fetuses with severe left Congenital Diaphragmatic Hernia (CDH) at UTHealth. UTHealth's success in this study (with an initial 5 patients) will determine the feasibility of UTHealth's future participation in multi-center trials of this intervention.

Inclusion Criteria:

• Pregnant women age 18 years and older
• 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
• O/E LHR < 30% - Gestation age at time of enrollment prior to 29 wks plus 5 days as determined by clinical information (LMP, 1st or 2nd trimester ultrasound) and evaluation of first ultrasound (measured at 270 to 296 weeks) at the time of surgery
• Gestational age at FETO procedure with O/E LHR < 30% at 27 weeks 0 days to 29 weeks 6 days as determined by clinical information (LMP) and evaluation of first ultrasound
• Patient meets psychosocial criteria
• Informed consent

Exclusion Criteria:

• Patient < 18 years of age
• 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 minutes of The Fetal Center at Children's Memorial Hermann 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 The Fetal Center at Children's Memorial Hermann Hospital.
• Right sided CDH or bilateral CDH, isolated left sided with O/E LHR ≥25% (measured at 18 weeks 0 days to 29 weeks 5 days) as determined by ultrasound[1]
• 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 post-operative 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
• There is no safe or technically feasible fetoscopic approach to balloon placement
• Participation in another intervention study that influences maternal and fetal morbidity and mortality or participation in this trial in a previous pregnancy