Which statement best describes fetal lung fluid?

• A. Clearance of lung fluid is complete at birth
• B. Volume approximates functional residual capacity after air breathing
• C. It is passively acquired from amniotic fluid
• D. It is produced by the placenta

Answer: (B)

Fetal lung fluid is produced by the fetal lungs and fills the airways during gestation. At birth, hormonal changes stimulate rapid reabsorption of most of this fluid so the lungs transition to air breathing. The amount of fluid that remains once breathing is established corresponds to the functional residual capacity, meaning the residual intrapulmonary fluid/air volume after a normal exhalation resembles the newborn’s FRC. So this statement correctly describes the transition: the remaining lung fluid volume after first breaths approximates FRC. The fluid isn’t completely cleared at birth, and it isn’t passively taken from amniotic fluid or produced by the placenta.