Pelvic fluid over 20mm is more serious and needs to be treated with medication. This is due to the fact that after ovulation, some follicular fluid will be discharged due to the discharge of eggs, so that the follicular fluid will gather in the rectal recess of the uterus and form a small amount of pelvic fluid, which can be found on the ultrasound. Such pelvic fluid is usually less than 20mm, and most women will slowly absorb it in their bodies before their menstrual period, so when they go for ultrasound after their menstrual period, such pelvic fluid will be gone. However, if the pelvic effusion is caused by pelvic inflammatory disease, on the one hand, the amount of effusion is more than 20mm, and on the other hand, the effusion will not be absorbed after menstruation, so only antibiotic treatment will be effective in this case.