21 weeks frequent fetal movement may be caused by physiological reasons, may also be pathological reasons, common analysis of the following aspects: 1, physiological reasons: 1, and the week of pregnancy: 21 weeks in the middle of pregnancy, at this time the fetal volume is relatively small, the uterine cavity activity space is sufficient, feel the fetal movement will be relatively frequent; 2, eating: at this time the pregnant woman’s body blood sugar content increases, the fetus will also replenish energy The fetal movement is relatively more; 3, sound stimulation: 21 weeks of pregnancy, the fetal hearing function has been established, when hearing the mother’s voice or music stimulation, will respond by way of fetal movement; 4, fetal own factors: some fetuses are more active in the uterine cavity, fetal movement is relatively frequent, as long as you maintain a certain pattern every day. Generally the fetus is more active at night, the most fetal movement is at 8-11 pm. Second, pathological reasons: 1, umbilical cord abnormalities: the most common umbilical cord around the neck, if the umbilical cord winding too tight, it will affect the blood flow through, resulting in fetal hypoxia, the early manifestation of fetal hypoxia is frequent fetal movement; 2, placental abnormalities: such as placental hypofunction, placenta praevia, placental abruption, such as placental abruption will block the supply of oxygen and nutrition to the fetus, there is increased fetal movement; 3, maternal diseases: such as Hypertension, anemia, heart disease, etc., may lead to insufficient maternal blood oxygen content, so that the fetus does not get enough oxygen supply, resulting in fetal hypoxia, which is manifested as frequent fetal movements, and if the hypoxia situation continues to be unimproved, fetal movements will gradually weaken or even disappear.