Fluid accumulation in the uterine cavity in early pregnancy may be caused by pre-eclampsia, endometritis or other gynecological diseases. 1. Pre-eclampsia: Pre-eclampsia caused by low progesterone level and abnormal embryo development will cause fluid accumulation in the uterine cavity, which is usually in large amount and requires further treatment under the guidance of a doctor. 2. Endometritis: Endometritis can also cause fluid buildup in the uterine cavity, and it is recommended to have regular checkups to observe changes in the amount of fluid. 3. Other gynecological diseases: Some gynecological diseases, such as vaginitis and pelvic inflammatory disease, can cause fluid accumulation in the uterine cavity. If there is fluid in the uterine cavity after pregnancy, it is recommended to go to the hospital for further examination to find out the cause of the disease and timely treatment, so as to avoid delaying the condition, which may affect the normal development of the fetus.