His nerves are connecting his brain to the rest of his body – traveling from the brain through the brainstem and down the spine, and beginning to extend into his torso and limbs.
Your baby's skeleton is changing too. The soft cartilage is starting to harden into bone. This happens first in the arms and legs.
Sensory development is picking up speed. Your baby's brain is designating special areas for smell, taste, hearing, vision, and touch. At this stage, your baby may be able to hear your heartbeat and voice, so read aloud or sing a happy tune.
Your baby may even be sucking his thumb now.
At about 18 weeks, you'll start to experience one of the most exciting parts of pregnancy: feeling your baby's movements. His flexing arms and legs may feel like gentle flutters at first. They'll become even stronger and more frequent in the weeks ahead.
At 20 weeks, your baby weighs a little more than 10 ounces and measures about 10 inches from head to heel (about the length of a banana).
This week is a big milestone – the halfway point in your pregnancy.