When performing endocrine hormone tests, the reference range for progesterone varies depending on the time of the test. In the mid-follicular phase, i.e., at the onset of menstruation during the follicular phase, the reference range is 0.99-4.83 mmol/L. In the mid-luteal phase, i.e., about 7-8 days before menstruation, the reference value for progesterone is 16.4-59.0 mmol/L. In menopausal women, the reference range at this time is 0.25-2.48 mmol/L. In the first trimester of pregnancy, the progesterone value is 15.0-161.4 mmol/L. As long as it is within this range, it is normal, but if it is low, it can also cause irregular menstruation.