This trial is testing a new prenatal treatment for babies with congenital diaphragmatic hernia (CDH). CDH is a birth defect where the diaphragm, the muscle that separates the chest from the abdomen, doesn't form correctly. This can cause the intestines and other abdominal organs to push up into the chest, and can prevent the lungs from developing properly. CDH can be diagnosed prenatally with ultrasound or MRI, and the severity can be estimated by the size of the lungs. This trial is testing a new treatment called fetoscopic endotracheal occlusion (FETO) where a balloon is placed