I often hear people of the older generation say: “big buttocks are good for childbirth”, which seems to have become the most famous saying, does this theory really hold true? The truth is – a big ass is not as good as a big pelvis for having a baby. The width and slope of the pelvis is what makes a woman with a large pelvic outlet and a wide and shallow shape good for childbirth, which cannot be seen from the outside alone. Some people have big buttocks but not big pelvis, just more body fat, which is not helpful for smooth delivery. On the contrary, if there is too much body fat, it is more likely that the fetus will be overweight and difficult to deliver. So, a big butt ≠ a good birth, a big pelvis is likely to be a good birth. In addition to pelvis, the key factors that affect the mother-to-be’s natural delivery are maternal labor force, fetal size and maternal mental and psychological factors. Labor force refers to the force that forces the fetus and its appendages out of the mother’s uterus. It includes the contraction force of the uterus, the contraction force of the abdominal muscles, the contraction force of the anal raphe and the contraction force of the diaphragm, among which the contraction force of the uterus is the main force of labor. The size of the fetus, the presence of malformations and the normal position of the fetus are directly related to the success of labor. Psychological factors such as fear of pain and rejection of natural childbirth can affect the balance and force of labor within the body, so the mother-to-be should maintain a good mental state during childbirth. Experts say that it is very unwise to choose cesarean section before delivery because of fear of pain, and when the conditions for vaginal delivery are available, it is better to choose vaginal delivery as much as possible. So the mother-to-be should be well prepared during pregnancy to improve the success rate of normal delivery.