So, what is progesterone, you may ask. P4 is a steroid hormone, is synthesized from pregnenolone, a derivative of cholesterol. It is produced in the adrenal glands, the gonads (more specifically after ovulation in the corpus luteum), the brain, and if you are lucky enough to be pregnant, the placenta. The levels of P4 should be low before ovulation. Then they will rise after. Like I said before, if it is higher than 5, that indicates ovulation, but doctors like to see it higher than 10. If you are pregnant, those levels should continue to rise. If you aren't pregnant, your P4 will drop and trigger the release of your lining, your period. Obviously this information is in regards to females during childbearing years. P4 levels are low in children and post-menopausal women. Men also have P4 levels that are comparative to adult females during the follicular phase of the menstrual cycle.
I copied this graph from Wikipedia. That's also the resource I used to explain P4.
All that said, my P4 is not nearly high enough to maintain a pregnancy. Which will probably lead to progesterone suppositories. I can't wait to start those bad boys!