Third trimester pregnancies do not usually have fluid in the uterus, nor do they have increased fluid in the uterus. Uterine fluid is not usually present in the third trimester of pregnancy. If there is an increase in fluid in the uterine cavity, it may be a sign of preeclampsia. At this time, the fluid is mainly blood, which flows out from underneath the attachment surface of the placenta and accumulates in the uterine cavity, forming a fluid collection. If there is an increase in fluid in the uterine cavity in the third trimester, it is important to go to the hospital for a checkup and closely monitor the changes in the fluid. If it is accompanied by an abnormal fetal heartbeat or if the bleeding is getting heavier and heavier, embryonic abruption may have occurred. If there is any abnormality, rational treatment under the guidance of the doctor.