There are many reasons why 40-year-old menstruation is dark, and they may be related to endocrine disorders and pregnancy-related diseases. 1. Endocrine disorders: If a woman’s ovarian function has decreased, the decrease in estrogen and progesterone levels in the body will affect the growth and development of the follicles and their discharge, which will cause the uterine lining to fail to peel off completely, resulting in low menstrual flow, darkness, and prolonged menstrual period. 2. Pregnancy-related illnesses: If a woman has a combination of preeclampsia or ectopic pregnancy and other adverse pregnancies, she may also experience low menstrual flow, darkening, lower abdominal swelling and other discomforts. The 40-year-old menstruation may also have other causes, it is recommended to go to the regular hospital, improve the blood human chorionic gonadotropin, ultrasound and other related examinations, clear cause of the disease under the guidance of the doctor targeted treatment.