The best time to correct the chest and knee position is 30 weeks of pregnancy. Before 28 weeks of gestation, the fetus is small, the amniotic fluid is relatively large, the fetus has a large range of motion in the uterus, and the position of the fetus is not constant. After 32 weeks of pregnancy, the fetus grows rapidly, the amniotic fluid is relatively less, the fetus is close to the uterine wall, and the fetal posture and position are relatively constant. Therefore, at 30 weeks of pregnancy, if abnormal fetal position is found, such as fetal breech position, or fetal transverse position, the fetal position can be corrected by chest and knee position.