During the fourth month gender becomes identifiable by ultrasound. At this time the baby sleeps, wakes, moves and kicks. Reflexes such as sucking and swallowing develop, and the baby may begin sucking his thumb. Eyebrows and eyelashes begin to appear. Bronchial tubes are branching. The baby's skin is pink, transparent and covered with soft hair. Sweat glands appear. The placenta is fully formed, and the umbilical cord continues to thicken. By the end of this month, the baby will be 6 - 7 inches long and weigh about 5 ounces.

During the fifth month, the baby is growing rapidly and is becoming much more active as the muscles are being strengthened. The baby sleeps and wakes at regular intervals. It is likely that you will feel movement at this time. The internal organs are maturing, and fat is being stored beneath the skin. Body hair is beginning to grow, and the skin is covered with vernix, a protective covering. Fingernails reach the tips of the fingers. Tonsils are developed, and milk teeth begin forming under the baby's gums. The baby's gall bladder begins producing the bile required for digestion. By the end of this month, the baby will be 8-12 inches long and weigh between ½ and 1 pound!

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.