Prenatal contraction bouts include the following characteristics: 1. Rhythmicity: usually the contractions are short and weak at the beginning of labor, gradually intensify, and then gradually become weaker after lasting for a period of time. That is, there is an interval after the contraction period, and then enter the contraction period after the interval; 2, symmetry: contractions usually start from both sides of the uterine horns to the middle, and then from the bottom of the uterus to the lower part of the uterus; 3, polarity: contractions gradually run from the bottom of the uterus to the lower part of the uterus, in a certain direction; 4, contraction effect: the uterus, through contractions, causes the fetus to descend gradually, which can move down the birth canal, the opening of the uterus increases, and the fetus is delivered.