The formation of fluid in the uterine cavity during pregnancy is related to many factors: 1. The fluid in the uterine cavity is considered to be caused by pre-eclampsia, mainly due to bleeding from the implantation of the gestational sac, or uterine bleeding caused by uterine dysplasia. The bleeding may also be due to insufficient hormone levels in the body after pregnancy or infection of the mother. It may also be due to immune rejection, which requires timely and symptomatic treatment. The treatment varies from one type of disease to another, so as not to affect the growth and development of the fetus. If treated in time, it basically will not have a great impact on the fetus. As long as the embryo is developing well, drugs such as progesterone can be taken for treatment, which can increase the progesterone level in the body and play a role in preserving the fetus.