There are many reasons for the formation of fetal peritoneal effusion, the common ones are fetal intra-abdominal tumor-like lesions, fetal fecal peritonitis, immune diseases, intrauterine infection of pregnant women, fetal chromosomal abnormalities and so on. 1. Fetal intraperitoneal tumor-like lesion: it can cause the fetus to exude fluid from the abdominal cavity and form peritoneal effusion, if this situation occurs, please consult a doctor in time to follow the doctor’s instructions to carry out reasonable and standardized diagnosis and treatment. 2. Fetal fecal peritonitis: it can lead to peritonitis caused by congenital malformation of the fetal intestine or lesions of the intestinal wall, such as intestinal perforation, which can further develop into peritoneal effusion. Therefore, please seek professional doctor for standardized treatment in time. 3. Immune diseases: pregnant women with immune diseases can cause abnormalities in the structure and function of the fetal immune system and lead to fetal peritoneal effusion, so follow the doctor’s instructions to control their own immune diseases during pregnancy. 4. Intrauterine infections: Intrauterine infections that occur during pregnancy or during labor and delivery may lead to successive infections in the fetus and thus create the possibility of fetal hydroperitoneum. Therefore, it is important to take precautions during pregnancy to avoid intrauterine infections. 5. Chromosomal abnormalities: mainly due to chromosomal abnormalities of both parents, usually there is no effective way to deal with, timely medical advice to give symptomatic treatment.