The thickness of the myometrium of the lower uterine segment in pregnant women is usually about 3mm normal. The lower part of the uterus is the narrow part of the uterus that softens after pregnancy, gradually stretches and thins, and then stretches into the birth canal after labor. The thickness of the myometrium of the lower uterine segment is usually around 3mm. If the thickness of the lower uterine muscle layer becomes thin, especially in women with a history of previous cesarean section, and the thickness of the lower uterine muscle layer is less than 3mm, there may be aura uterine rupture, uterine rupture, etc., which may result in hemorrhagic shock, or even the need for uterine resection in the late stages of pregnancy or vaginal delivery, which can jeopardize the lives of both mother and child. Therefore, once a pregnant woman finds that the thickness of the myometrium in the lower part of the uterus has become thin, she should consult an obstetrician in a regular hospital immediately, and under the guidance of the obstetrician, she should carry out all kinds of examinations and treatments, so as to avoid any adverse consequences.