The rationale for fetal therapy in severe congenital diaphragmatic hernia is to restore 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. European colleagues have developed intrauterine endoscopic techniques (fetoscopy) to position and remove endoluminal tracheal balloons in utero (fetoscopic endotracheal occlusion = FETO). Recently, the Belgium group published summary results of FETO showing an improved survival in 175 patients with isolated left CDH from 24% to 49%. Our goal with this pilot study is to study the feasibility of implementing FETO therapy in the most severe group of fetuses with left CDH (O/E LHR < 30%). which will be considered in two subgroups. Those with and O/E LHR <25% (severe group) and those with an O/E between 25 to <30% (less severe group).