Prospective Registry for Long-term Outcomes Following FETO in Severe Left and Right CDH

Inclusion Criteria: * Pregnant women age 18 years and older * Singleton pregnancy * Normal Karyotype, chromosomal microanalysis (CMA) with non-pathologic variants, whole exome sequencing (WES) or whole genome sequencing (WGS). Results by fluorescence in situ hybridization (FISH) will be acceptable if the patient is \> 26 weeks gestation. * Gestational age at enrollment is prior to 29 weeks + 6 days gestation. * Intrathoracic liver herniation: * Isolated left CDH with o/e LHR \< 30% at enrollment (18wks + 0 days to 29wks + 5 days gestation). * Isolated right CDH with o/e LHR ≤ 45% at enrollment (18wks + 0 days to 29wks + 5 days gestation). * Cervical length by transvaginal ultrasound ≥ 20 mm within 24 hours prior to FETO procedure. * Patient meets psychosocial criteria. * Informed consent understood. Exclusion Criteria: * Patient \< 18 years of age * Multi-fetal pregnancy * History of natural rubber latex allergy * Preterm labor, cervix shortened (\<20 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: 1. Inability to reside within 30 minutes of Johns Hopkins Hospital Center for Fetal Therapy. 2. The 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 Johns Hopkins Hospital Center for Fetal Therapy. * Bilateral CDH, isolated left sided CDH with O/E LHR ≥ 30% (18wks + 0 days to 29wks + 5 days gestation), isolated right sided CDH with O/E LHR \> 45% (18wks + 0 days to 29wks + 5 days gestation), as determined by ultrasound. * No liver herniation into thoracic cavity. * Additional fetal anomaly and chromosomal abnormalities by ultrasound, MRI, or echocardiogram at the fetal treatment center. Exclude chromosomal abnormalities, associated anomalies recognized to alter survival prognosis (i.e., CDH and congenital heart disease) or presence of an underlying genetic syndrome (i.e., Fryns). * 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 anomalies 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.