From the ninth week of development until birth, the growing human is referred to as a fetus. After approximately nine months, a human infant is born. A number of dramatic changes occur in an infant’s lungs and circulatory system to allow the baby to breathe and circulate blood completely on his or her own. Previously, the baby was totally dependent on the mother through the umbilical cord connection with the placenta. At birth, this physical connection ends as the baby moves into another stage of the human life cycle.