The condition Little Baby Derrevere has is called Congenital Diaphragmatic Hernia. He has a hole on the left side of his diaphragm allowing just the stomach to protrude into the left side of his chest. He is otherwise perfectly normal on ultrasound. His heart and lungs have normal structure and function. How a baby will do after birth is sometimes unpredictable, but if they have good lung volumes and a normal heart they tend to do much better. The concern is that if there is not enough room in the chest for the lungs to grow CDH may cause the lungs to be small and the pulmonary arteries to have high blood pressure. Approximately 1:2500 children are born with CDH. It is just as frequent as spina bifida or cystic fibrosis. CDH happens during the 7th to 10th week of gestation. There is no known cause of CDH except for a 2% chance of having another child with CDH. There is an overwhelming amount of information out there an not all of it is reliable. I prefer the website below for those who are interested, however the pediatrician in me doesn't at all mind answering your questions!

CHERUBS- The Association of Congenital Diaphragmatic Hernia Research, Awareness and Support

This is a cartoon showing basic anatomy.