In the second trimester, the fetus has a wide range of activities in the uterine cavity and can exist in various postures in the uterine cavity. As the fetus grows and its gestational age increases, the fetus will gradually lie in a head-down supine position until delivery at the end of pregnancy. Due to the slender uterus, umbilical cord traction, polyhydramnios, fetal malformation, etc., or the mother-to-be is a multiparous woman, the abdominal wall is loose, and the fetus moves widely in the uterine cavity, resulting in the fetus appearing in breech position, transverse position, etc., which is called dislocation. At the end of pregnancy, pregnant women who are in the breech position will feel that their chest is particularly tight.