Normal menstrual cycle, but heavy bleeding or prolonged duration
・ Uterine myomas
・ Adenomyosis
・ Coagulation disorders

Normal menstrual cycle, but abnormal bleeding between periods
・ Endometrial polyps
・ Cervical polyps
・ Endometritis

Irregular menstruation (cycle, duration, and flow varies)
・ Ovulatory dysfunction
・ Polycystic ovarian syndrome
・ Hyperprolactinemia
・ Thyroid disease

No menstruation for more than 3–6 months
・ Ovulatory dysfunction
・ Hypothalamic secondary amenorrhea
・ Premature ovarian insufficiency
・ Intrauterine adhesions

Abnormal bleeding
・ Abnormal pregnancy or pregnancy-related complications: early pregnancy, threatened abortion, ectopic pregnancy, molar pregnancy, etc.
・ Malignant diseases: endometrial cancer, cervical cancer, ovarian cancer, etc.
・ Reproductive tract infections: cervicitis, endometritis, atrophic vaginitis.
・ Improper medication use: incorrect use of contraceptive pills, use of emergency contraception.
・ Foreign bodies: e.g., displaced intrauterine device (IUD).

The main cause is an abnormality in the menstrual regulatory system (the hypothalamic–pituitary–ovarian axis), which leads to failure of ovulation or inadequate luteal function. It is commonly seen in adolescent girls, women in the menopausal transition, and women of reproductive age.
‍

・ Vigorous exercise
・ Eating disorders
・ Stress
・ Idiopathic hypogonadotropic hypogonadism
・ Lactational amenorrhea
・ Breastfeeding without menstruation
・ Pituitary adenoma or other pituitary tumor
・ Other conditions:
     - Polycystic ovary syndrome
     - Hyperthyroidism or hypothyroidism; hormone-secreting tumors (adrenal or ovarian)
     - Chronic liver or kidney disease
     - Cushing's disease
     - Premature ovarian insufficiency (may be related to autoimmune, genetic, surgical, idiopathic causes, or associated with medications or radiation)
‍