Is pelvic fluid 2.9cm serious? Generally speaking, it is not. In the female reproductive system, pelvic effusion has the following two possibilities during the menstrual cycle: one is physiological pelvic effusion and the other is pathological pelvic effusion. When menstruation or follicular phase, due to the backflow of menstrual blood and the discharge of follicular fluid caused by ovulation, there can be fluid in the pelvic cavity at this time, and it may reach 2.9 cm, and it depends on whether the pelvic fluid persists in the future. The physiological pelvic fluid can be slowly absorbed by itself, but if this pelvic fluid persists and is accompanied by pain in the lower abdomen or purulent leucorrhea, it may be a pelvic inflammatory disease or other gynecological disease, which requires timely and symptomatic treatment at the hospital.