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Your Developing Baby, Week by Week

Your baby begins as a tiny cluster of cells, but during the nine-month process of pregnancy she becomes an amazing baby with facial features, a beating heart and kicking legs. Find out what's happening with baby's development week by week.
week 23 Week 23

Billions of brain cells will develop in your baby's brain over the next couple of weeks. These will control all of your baby's movements and sensory, and basic life functions like breathing. Also around this time, some major changes are happening with your baby's lungs. Surfactant is being produced, a substance that enables the air sacs to inflate and the lungs to fully expand. Right now he's still breathing amniotic fluid, but when he's born he'll be ready for air.