Subjects to be enrolled in this study are pregnant women whose unborn baby has been diagnosed with severe congenital diaphragmatic hernia (CDH). CDH is a birth defect occurring early in pregnancy. It is characterized by the development of a hole in the diaphragm, the breathing muscle that separates the chest from the abdomen. As a result, the intestines and other organs in the baby's abdomen can move into the chest and press on the developing lungs. CDH is a serious condition which prevents the fetal lungs from developing normally.