Pelvic fluid does not cause menstrual cramps, the main cause of menstrual cramps is most likely due to abnormal changes in the thickness of the uterine lining or functional bleeding of the uterus. The presence of pelvic fluid in a woman’s pelvic cavity reflects the presence of pelvic inflammatory disease, which does not have a direct impact on the endometrium, and there is no inevitable relationship between irregular menstruation and pelvic fluid. For women who have missed periods, an ultrasound is needed to check the thickness of the endometrium in the uterus after the period or menstrual period has cleared, to determine if abnormal thickness changes in the endometrium are the cause of the problem. Hormone levels can also be checked, as a certain degree of hormone disruption in the body can lead to abnormal changes in the thickness of the lining of the uterus, which can cause irregular periods.