“Your baby is now weighing about 2 pounds and measuring about 32cm. As the blood vessels in the lungs began last week, the air sacs in the lungs begin this week. The lungs begin to secrete surfactant which covers the inner lining of the air sacs which then allows the lungs to expand normally during breathing. Your baby will also begin to have brain wave activity, and will start to hear and respond to noises, both internally and externally.”