Fetal pulmonary cystadenoma is a benign cystadenoma that forms in the fetal lung during development, and the pathogenesis is unclear. Although fetal pulmonary cystadenoma is benign, if the cystadenoma is too large, it may not only cause compression of the surrounding tissues, but also cause displacement of the fetal heart or lead to edema in the fetal lung. Whether a fetus with a cystadenoma can be preserved depends on the size of the cystadenoma and whether there are symptoms of compression such as pleural effusion and pericardial effusion. If the fetus has a small, slow-growing cystadenoma and does not cause surrounding tissue compression, heart displacement, or fetal edema, the fetus can be retained in this case. After the fetus is born, the prognosis is mostly good with appropriate treatment and, if necessary, surgical removal depending on the specific case. However, if the cystadenoma is large and has compressed the fetal heart, causing fetal pulmonary edema, the prognosis for the fetus in such cases is not good. In general, the growth of cystadenoma may slow down after 28 weeks, even if the mass is no longer visible on ultrasound. However, it is still recommended to have a CT or MRI review of the chest after birth, and some children may have cystic adenoma after birth, which may require surgery. It is recommended to follow up with the pediatric thoracic surgery department after birth and review the chest CT or MRI as appropriate to further clarify the diagnosis.