During the sixth month, the brain is in a period of rapid development. The baby's skin is wrinkled, red and covered with a vernix covering. Eyelashes and eyebrows are well formed. The bones are becoming solid. The eyelids part and begin to open. Toenails begin to grow. The baby is able to hiccup. Brown fat, which keeps the baby warm at birth, is forming. The baby is almost fully formed, but the lungs are not yet fully developed. By the end of this month, the baby will be 11-14 inches and weigh about 1½ to 2 pounds.