Final answer:
False. The lungs of the fetus are not filled with air late in pregnancy; they contain amniotic fluid, mucus, and surfactant. The first true breath with air inhalation occurs only after birth when the baby is exposed to the external environment and starts to breathe on its own.
Step-by-step explanation:
The question of whether the lungs of the fetus are filled with air late in pregnancy is best answered as false. Fetal lungs are filled with amniotic fluid, mucus, and surfactant rather than air. During the late stages of pregnancy, the fetal lungs are developing and preparing for the critical first breath after birth. The lung expansion necessary for the newborn to breathe on its own is facilitated by the production of pulmonary surfactant, which develops more significantly around the eighth month of pregnancy and continues to mature even after childbirth.
Fetal breathing movements may begin around week 20 as practice, but these are not actual 'breaths' with air. The placenta provides the necessary oxygen to the fetus through the umbilical cord. After birth, contractions and the physical compression of the baby as it passes through the birth canal help expel the fluid from the lungs, and the change in environment triggers the infant's first breath, which inflates the lungs.