Progesterone is a Progestin produced primarily from enzymatic metabolism of Pregnenolone. It is enzymatically converted to 17-Hydroxy Progesterone and 11-Deoxycorticosterone. It is secreted by both the gonads and the adrenal glands. It is bound to Cortisol Binding Globulin and Albumin, but a small percentage is present in the "Free" bioactive form. It is excreted into the urine as its conjugated and unconjugated forms and as Pregnanediol (conjugated and unconjugated). This assay measures the conjugated and unconjugated forms of Progesterone. Progesterone is responsible for cellular changes in the cervix, vagina, and uterus. Levels are lowest in the follicular phase and increase rapidly following the luteal surge. Progesterone increases greatly during pregnancy. Measurement of Urine Progesterone can be useful to monitor fertility, corpus luteum function, endometrial development, and be helpful in in-vitro fertilization patients yielding an integrated look of Progesterone activity over a 24-hour period.