Although the exact cause of JIA is unclear, as children grow older, symptoms often improve, which means they can live a normal life. A progesterone blood test is conducted to ascertain how much of the progesterone hormone is within a sample of blood. This female hormone is produced whenever a mature egg is released from an ovary within a process generally known as ovulation. This hormone helps to prepare the endometrium (uterine lining) to just accept the egg if sperm fertilizes it. If the egg goes without getting fertilized, menstrual bleeding occurs and progesterone levels drop.