During a woman’s pregnancy, the fetal position of the baby actually refers to the relationship between the baby’s first exposed part and the mother’s pelvis. For example, the left posterior occipital position means that the baby’s occipital bone is located at the back of the mother’s pelvis, which is the orientation of the front of the face. In general, if the woman’s pelvis is wide and the baby is small, for example, weighing less than 3,500g, the contractions will strengthen after delivery and promote the rotation of the fetal head into a left occipitofrontal position, and then the baby will be delivered vaginally. In general, the baby’s head passes through the mother’s birth canal with the smallest diameter, because the mother’s birth canal is a bony birth canal. The bony birth canal has very little mobility, and the baby can only be delivered with the smallest diameter by changing the shape of the skull by overlapping the skull of the fetal head, which means changing the shape of the baby’s head to fit the mother’s birth canal. Therefore, if the fetal head is large, the fetal weight is large, for example, more than 4000g for a huge baby, and the persistent left posterior occipital position is difficult to deliver vaginally, it can cause the phenomenon of difficult vaginal delivery.