Around 30 weeks, the growth of the brain markedly increases. Most systems are well developed, and the fetus can see and hear. A baby may survive if born this early, although the lungs may still be immature. Update Date: 10/24/2006Stuart Bentley-Hibbert, M.D., Ph.D., Department of Radiology, Weill Cornell Medical Center, New York, NY. Review provided by VeriMed Healthcare Network.