The reason why the fetal movement becomes less in 31 weeks of pregnancy may be due to the increased sleep time of the fetus or intrauterine hypoxia of the fetus. 1. Fetal sleep time increases: if the baby temporarily reduces fetal movement, the fetus will reduce fetal movement in the sleep state. 2. Fetal intrauterine hypoxia: in the middle of pregnancy, if the decrease in fetal movement is obvious, you need to go to the hospital in time for ultrasound examination and fetal heart monitoring to find out whether it is due to intrauterine hypoxia caused by the umbilical cord around the neck, decreased placental function, and low amniotic fluid volume. Fetal movement in the 31st week of pregnancy needs to go to the hospital in time to make a clear diagnosis, the doctor according to the specific situation, to formulate individualized diagnosis and treatment plan, so as not to affect the health of the fetus.