Submembranous effusion is usually taken as an indicator of preeclampsia, which may be caused by unstable implantation of the fertilized egg, abnormal rheumatological and immune indicators, and external factors. 1. Unstable implantation of fertilized egg: when the gestational sac is implanted in early pregnancy, due to unstable implantation, it causes bleeding of capillaries in the local meconium, which may result in submembranous effusion. 2. Abnormal rheumatic immunity index: this condition is easy to form a small amount of local hemorrhage, and also easy to cause submembranous effusion. 3. External factors: If a pregnant woman is hit by external forces, resulting in contractions, it may also cause the fetal membranes to detach from the uterine wall, resulting in a small amount of bleeding around. It is recommended that pregnant women maintain a good state of mind after the emergence of fetal membrane effusion, timely medical treatment, under the guidance of doctors, improve the relevant examination, clear causes, symptomatic treatment.