Baby’s Lung Development in Pregnancy

By 24–28 weeks of pregnancy, your baby’s lungs are forming more air sacs (alveoli) and starting to produce surfactant, but they are still not ready for full breathing outside the womb.

1. Early Development

• The lungs begin forming around week 4–6 of pregnancy.
  • By the end of the first trimester, the basic structure is present but not yet functional.

2. Development of Air Sacs (Alveoli)

• Between 24–28 weeks, the lungs begin forming alveolar sacs—tiny air sacs where oxygen exchange will eventually occur.
  • These sacs continue multiplying until birth and even into early childhood.

3. Surfactant Production

• Around 24 weeks, special lung cells start producing surfactant.
  • Surfactant coats the alveoli and prevents them from collapsing by reducing surface tension.
  • At this stage, only small amounts are present—not enough for independent breathing.

4. Breathing Movements in the Womb

• Babies begin making 'practice breaths' by moving the chest wall and diaphragm.
  • These movements help strengthen muscles needed for breathing after birth.
  • The lungs are filled with amniotic fluid at this stage, not air.

5. Still Not Ready for Full Breathing

• The lungs are still immature between 24–28 weeks.
  • If a baby is born at this stage, they usually need medical help such as oxygen and surfactant therapy.
  • Each week of development increases their chance of survival.

6. Importance of This Stage

• Development of alveoli and the beginning of surfactant production are critical milestones.
  • Over the next weeks, surfactant levels rise, preparing the lungs for life outside the womb.

Summary

By 24–28 weeks, the baby’s lungs are developing essential air sacs and beginning to produce surfactant. Although these changes are vital, the lungs are still too immature for full breathing without medical support. Each additional week of growth significantly improves lung function and readiness for birth.