Progesterone is reduced at the C-3 and C-20 groups, hydroxylated to polar derivatives at C-6 and C-10, and conjugated almost entirely with glucuronide in human and rabbit liver by UDP glucuonyltransferase. The main metabolite is 5β-Pregnane-3α,20α-diol glucuronide. Glucuronic acid is attached via a glycosidic bond to the substance, and the resulting glucuronide, which has a much higher water solubility than the original substance, is eventually excreted by the kidneys. The assessment of 5β-Pregnane-3α,20α-diol glucuronide may be applied to detecting ovulation, assessing the function of corpus luteum, and monitoring early pregnancy.