The purpose of this research is to determine if babies who undergo a Fetoscopic Endoluminal Tracheal Occlusion (FETO) procedure survive more often and have less long-term complications than babies who have similarly severe Congenital Diaphragmatic Hernia (CDH) that have not had the FETO procedure performed during pregnancy

Inclusion Criteria:

• Singleton pregnancy
• Normal fetal karyotype with confirmation by culture results, CMA with non-pathological variants, WES or WGS. Results by fluorescence in situ hybridization (FISH) will be acceptable if the patient is > 26 weeks
• Gestational age at enrollment prior to 29 6/7 weeks
• Intrathoracic liver herniation Isolated left CDH with O/E LHR < 30% at enrollment (18 0/7 to 29 5/7 weeks.) Isolated right CDH with O/E LHR < 45% at enrollment (18 0/7 to 29 5/7 weeks).
• Cervical length by transvaginal ultrasound > 20 mm within 24 to 48 hours prior to FETO procedure
• Patient meets psychosocial criteria
• Informed consent understood

Exclusion Criteria:

• Multi-fetal pregnancy

• History of natural rubber latex allergy

• Preterm labor, cervix shortened (<20 mm at enrollment or within 24 to 48 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 Mayo Clinic. 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 Mayo Clinic.

• Bilateral CDH, isolated left sided CDH with O/E LHR 30% (measured at 180 to 295 weeks), isolated right sided CDH with O/E LHR > 45% (measured at 180 to 295 weeks), as determined by ultrasound.

• No intrathoracic liver herniation

• 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.

• Maternal contraindication to fetoscopic surgery or severe maternal medical condition in pregnancy

• History of incompetent cervix with or without cerclage

• Placental abnormalities (previa, abruption, accreta) 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

Pregnant patients with fetuses affected by congenital diaphragmatic hernia meeting the inclusion criteria above-mentioned and not meeting exclusion criteria.