In the early embryonic period, the thoracic and abdominal cavities are connected to each other, and the diaphragm gradually forms to separate the thoracic and abdominal cavities by the time the embryo is about three months old; if there is an obstruction in the formation of the diaphragm, abdominal organs can easily enter the thoracic cavity through the gap. This is why diaphragm formation occurs in the first four months of pregnancy.