Contraction of uterus:
The better the uterine contraction intensity, the faster the production process will be, and the contraction intensity is restricted by the age of expectant mothers, muscle tension and elasticity, fetal weight and other conditions.
According to our usual concept, the larger the pelvis, the greater the chance of spontaneous delivery. Medical theory also holds that mothers-to-be will have no problem delivering when their pelvic diameter is above 9.8 centimeters. Natural delivery when the pelvic diameter is less than 9.2 centimeters is less likely. The diameter of the middle pelvis can be judged by X-ray. But in real life, the size of the pelvis is not the decisive factor. Sometimes the pelvis is large enough to have difficulties in childbirth. Sometimes the pelvis is not large because the fetus is small, it will also give birth smoothly.
The average weight of the newborn is 2.8 kg to 3.5 kg, in this range of delivery, the labor process will be relatively shorter, easy to spontaneous delivery; if the weight of the newborn exceeds 3.5 kg, the pelvis of the parturient is not large enough, it may occur dystocia.