Most women menstruate once in about 28-30 days, and the medically normal menstrual cycle allows for a range of 21-35 days, so a period of 25 days is within the normal range. Some people have a 25-day menstrual cycle, some have a 35-day cycle, and there is nothing to worry too much about as long as they have their own regularity. However, if your period used to be 30 days and now it is 25 days, this is a shortening of the menstrual cycle and may indicate the occurrence of certain diseases. For example, patients with uterine fibroids may have shortened menstrual cycles, increased menstrual flow, and longer periods. In the case of a woman in her 40s, if her menstrual cycle, which was previously around 28-30 days, now becomes 25 days, it may also be a sign of ovarian decline. Ovarian decline can manifest as a shortening of the menstrual cycle followed by a lengthening of the menstrual cycle, in which case it is recommended to assess the reserve function of the ovaries. In addition, thyroid disorders may affect the menstrual cycle. In addition, sedatives, antidepressants, work or mental stress may affect the secretion of brain chemicals and the release of female hormones from the pituitary gland, thus affecting the menstrual cycle. If you have not had your period for 1 month, it depends on the specific age of the woman to analyze it specifically. In the case of women who have not had sex during puberty, especially young girls who have just started menstruating, the endocrine axis that regulates menstruation is not yet well developed and irregularities in the menstrual cycle may occur. Most of them will become regular as they get older. Some women may have long menstrual cycles, such as once every 2-3 months, or even longer, with low menstrual flow, and may be combined with obesity and hirsutism. Most of these women have polycystic ovary syndrome and need to be examined in the hospital to decide whether or not to take medication based on whether or not they have fertility requirements. For women who are sexually active, if you have not had your period for 1 month, you should first rule out the possibility of pregnancy. You can take an early pregnancy test and if it is positive, you should consider pregnancy and go to the hospital for further examination. If the early pregnancy test is negative, you can treat with progesterone. For perimenopausal women, if you do not have a period, you can also treat with progesterone to see if you can still have a period after ruling out the possibility of pregnancy, or you can check the hormone level to understand the function of the ovaries. In addition, menstruation can also be affected by mental factors, such as exams, stressful work, frequent business trips, etc. If these factors are removed, most menstruation can return to normal.