What Week Do Baby’s Lungs Develop?

As an expecting mother, you want to ensure your baby is healthy and developing correctly. One crucial aspect of fetal development is the growth and maturation of their lungs. But when do baby’s lungs develop? The answer is a bit more complicated than a single week, as lung development is a process that occurs throughout pregnancy.

Early Lung Development

During the first few weeks of pregnancy, the respiratory system begins to form. At around week four, the trachea and bronchi start to develop from the fetal tissue. By the end of the embryonic stage, which lasts until week eight, the lungs have formed as two buds in the chest cavity.

By week nine, the bronchi begin to branch off into smaller bronchioles. The bronchioles continue to divide and branch throughout pregnancy, forming a highly complex network of airways. At this stage, the lungs are still filled with fluid and are not yet functional.

Mid-Pregnancy Lung Development

Around week 16, the baby’s lungs start to produce surfactant, which is a substance that helps keep the air sacs in the lungs open. This is a critical stage in lung development, as the lack of surfactant can lead to respiratory distress syndrome in premature babies.

By week 20, the baby’s lungs have developed enough to begin making breathing movements. These movements are not actual breathing, but rather practice for when the baby is born and needs to take their first breaths.

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Late Pregnancy Lung Development

During the final weeks of pregnancy, the baby’s lungs continue to mature rapidly. The air sacs in the lungs become more numerous and smaller, which increases the surface area for gas exchange. The blood vessels in the lungs also grow and become more complex.

By week 36, the baby’s lungs are considered fully developed and ready for life outside the womb. However, lung development can vary from baby to baby, and some babies may need extra support after birth to help their lungs function correctly.

What Week Do Baby'S Lungs DevelopSource: bing.com

Factors That Affect Lung Development

Several factors can impact the development of a baby’s lungs during pregnancy. These include:

  • Maternal smoking
  • Maternal exposure to pollutants
  • Maternal infections
  • Maternal nutrition
  • Preterm birth

It’s essential to take care of your health during pregnancy to ensure your baby has the best chance of developing healthy lungs.

Frequently Asked Questions

Q: Can lung development be delayed or impaired?

A: Yes, several factors, such as maternal smoking, pollution exposure, or infections, can impact lung development.

Q: Can premature birth impact lung development?

A: Yes, premature babies may have underdeveloped lungs and may need extra support after birth to help them breathe.

Q: What is surfactant?

A: Surfactant is a substance produced by the baby’s lungs that helps keep the air sacs open and prevents them from collapsing.

Q: When do babies start making breathing movements?

A: Around week 20 of pregnancy, babies begin making breathing movements to practice for when they are born and need to take their first breaths.

Q: When are baby’s lungs fully developed?

A: By week 36, baby’s lungs are considered fully developed and ready for life outside the womb.


In conclusion, lung development is a critical aspect of fetal development that occurs throughout pregnancy. From the formation of the trachea and bronchi to the production of surfactant and the growth of blood vessels, a lot happens in the nine months leading up to birth. Taking care of your health during pregnancy can help ensure your baby has healthy lungs and a healthy start to life.

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By administrator

I am a child development specialist with a strong passion for helping parents navigate the exciting and sometimes challenging journey of raising a child. Through my website, I aim to provide parents with practical advice and reliable information on topics such as infant sleep, feeding, cognitive and physical development, and much more. As a mother of two young children myself, I understand the joys and struggles of parenting and am committed to supporting other parents on their journey.

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