Weeks 21 to 25
During the second half of pregnancy, the fetus becomes increasingly aware of the world outside. It is startled by sudden noises, and is thought to be capable of feeling pain after 5-6 months. Rapid eye movements, associated with dreaming sleep in adults, begin at 21 weeks (the 23rd week of pregnancy). The fetus looks transparent, as it doesn't yet have any fat under its skin.
