Despite advances in prenatal diagnosis and postnatal therapies, including ECMO (Extracorporeal Membrane Oxygenation), inhaled nitric oxide therapy, and ventilator strategies that minimize ventilator-induced lung injury, morbidity and mortality rates for babies with severe CDH remain high. The rationale for fetal therapy in severe CDH is to promote adequate lung growth for neonatal survival. Prenatal tracheal occlusion obstructs the normal egress of lung fluid during pulmonary development leading to increased lung tissue stretch, increased cell proliferation, and accelerated lung growth. The investigator's goal with this pilot study is to study the feasibility of implementing Fetoscopic Endoluminal Tracheal Occlusion (FETO) therapy in the most severe group of fetuses with left CDH (LHR O/E < 25%).