This week, your baby measures over 16 inches long. He weighs about 3.3 pounds and is heading into a growth spurt. He can turn his head from side to side, and his arms, legs, and body are beginning to plump out as needed fat accumulates underneath his skin. He's probably moving a lot, too, so you may have trouble sleeping because your baby's kicks and somersaults keep you up. Take comfort: All this moving is a sign that your baby is active and healthy.