According to Babycenter.com:
The network of nerves in your baby's ears is better developed and more sensitive than before. He may now be able to hear both your voice and your partner's as you chat with each other. He's inhaling and exhaling small amounts of amniotic fluid, which is essential for the development of his lungs. These so-called breathing movements are also good practice for when he's born and takes that first gulp of air. And he's continuing to put on baby fat. He now weighs about a pound and two-thirds and measures 14 inches (an English hothouse cucumber) from head to heel. If you're having a boy, his testicles are beginning to descend into his scrotum — a trip that will take two to three days.
According to Fitpregnancy.com:
Your baby weighs about 1 1/2 pounds and has undergone a growth spurt in the past few weeks. From weeks twenty to twenty-eight, she almost doubles in height and now would be about a foot tall if she could stand. This week marks a major milestone in your baby's hearing and sight. Your baby's hearing system (cochlea and peripheral sensory end organs), which began fine development during week eighteen, is now completely formed, and over the next few weeks, she'll become increasingly sensitive to sound. In about a month, you'll feel her jump if she hears a sudden loud noise. Sound passes easily into your uterus, which helps her ears develop. Her eyes are almost fully formed. Did you know that all babies have blue eyes in the womb, no matter what their genetic inheritance is? A baby's eyes don't get their final color until a few months after they are born. The air sacs of the lungs, called alveoli, will be developed by the end of this week and will begin to secrete a substance called surfactant that keeps the lung tissue from sticking together.