TTN is a benign disorder, and pathologic conditions must be excluded. (UpToDate)
"Transient tachypnea of the newborn is the most common cause of neonatal respiratory distress, constituting more than 40 percent of cases. A benign condition, it occurs when residual pulmonary fluid remains in fetal lung tissue after delivery. Prostaglandins released after delivery dilate lymphatic vessels to remove lung fluid as pulmonary circulation increases with the first breath. When fluid persists despite these mechanisms, transient tachypnea of the newborn can result. Risk factors include maternal asthma, male sex, macrosomia, maternal diabetes, and cesarean delivery.
"The clinical presentation includes tachypnea immediately after birth or within two hours, with other predictable signs of respiratory distress. Symptoms can last from a few hours to two days. Chest radiography shows diffuse parenchymal infiltrates, a “wet silhouette” around the heart, or intralobar fluid accumulation."
See this radiograph from eMedicine (https://emedicine.medscape.com/article/414608-media)