The amniotic sac is a structure surrounded by the amniotic membrane of the fetal appendage, inside of which is the fetus and amniotic fluid, providing a place for the fetus to grow and develop in the abdomen. The amniotic sac provides space and a constant temperature for fetal growth and development. As the amniotic sac is filled with amniotic fluid, this fluid has a cushioning effect on the fetus, preventing extrusion of the fetus during pregnancy, and also preventing fetal hypoxia and fetal distress due to direct compression of the muscular wall of the uterus or the fetus against the umbilical cord. During labor contractions, amniotic fluid can make the contraction pressure evenly distributed, avoiding fetal distress caused by localized pressure on the fetus. When the body is ready for labor in late pregnancy, the amniotic sac ruptures and amniotic fluid flows out of the vagina. If you notice any abnormalities during pregnancy it is recommended that you seek prompt medical attention and follow the doctor’s instructions for examination and treatment.