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.