Which statement best differentiates respiratory distress syndrome (RDS) from transient tachypnea of the newborn (TTN) in terms of onset and pathophysiology?

• A. TTN is caused by surfactant deficiency and presents immediately after birth, while RDS occurs from delayed clearance of fetal lung fluid in term infants.
• B. RDS is due to surfactant deficiency causing alveolar collapse and typically presents within minutes to hours after birth in prematurity; TTN results from delayed clearance of fetal lung fluid, often in term or late preterm infants, with onset within hours after birth.
• C. Both conditions have identical onset and pathophysiology; onset is within minutes but TTN has earlier onset.
• D. RDS occurs only in term infants and TTN only in preterm; onset times are the same.

Answer: (B)

The key distinction is what goes wrong in the lungs and when it shows up after birth. Respiratory distress syndrome happens because there isn’t enough surfactant in immature lungs. Surfactant lowers surface tension so the tiny air sacs (alveoli) stay open; without it, alveoli collapse, making breathing laborious and gas exchange poor. This deficit is most common in preterm infants, so signs of RDS typically appear within minutes to hours after birth as oxygenation worsens.

Transient tachypnea of the newborn is due to delayed clearance of fetal lung fluid after birth. The lungs are usually structurally mature, but fluid lingers in the airways, causing rapid breathing and mild-to-moderate distress. TTN is more often seen in term or late preterm infants and is frequently associated with cesarean delivery or rapid birth transitions. The onset is still within hours after birth, but the underlying problem is impaired fluid reabsorption rather than surfactant deficiency.

Imaging differences support this distinction: RDS tends to show a diffuse granular or reticulogranular pattern with low lung volumes and air bronchograms, reflecting widespread atelectasis. TTN often shows mild hyperinflation with prominent central markings, reflecting retained fluid and airway edema rather than diffuse collapse.

So, the best differentiation is that RDS arises from surfactant deficiency causing alveolar collapse in prematurity with early onset after birth, while TTN stems from delayed clearance of fetal lung fluid in term or late preterm infants, with onset in the early hours after birth.