When Do the Lungs Develop?
The lungs develop gradually and are among the last organs to mature. They produce surfactant from around 24–28 weeks and are usually ready for breathing air by about 36–37 weeks, though development continues after birth.
Lung development stages
- Airway structures form through the second trimester.
- Surfactant — which keeps the lungs open — appears from about 24–28 weeks.
- Lungs are usually ready for air by about 36–37 weeks.
Why prematurity affects breathing
Babies born early may have immature lungs and need breathing support. If preterm birth is likely, doctors may give steroid injections to speed lung maturity.
Full readiness near term
By full term the lungs are ready to breathe air, though they keep developing new air sacs after birth.
Frequently asked questions
When are my baby's lungs fully developed?
Usually ready for air by about 36–37 weeks, with development continuing after birth.
What is surfactant?
A substance that keeps the tiny air sacs open so the lungs can work; it appears from about 24–28 weeks.
What if my baby is born early?
Preterm babies may need breathing help; steroids before a preterm birth can speed lung maturity.
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See exactly how your baby grows in the complete 40-week guide.
40-Week GuideJoin The CircleReferences
- WHO. Antenatal care recommendations. who.int
- ACOG. Fetal development. acog.org
- NHS. You and your baby, week by week. nhs.uk
- Tommy's. Baby movements & development. tommys.org
- CDC. During Pregnancy. cdc.gov