There is no evidence of side effects or harm from fetal heartbeat devices. Under normal circumstances, fetal heart rate monitors do not affect the fetus or the mother. Fetal heart rate monitor mainly detects the fetal heart rate and fetal movement, and can be used by mothers without any worry. Fetal heart rate monitor is based on the Doppler principle to check whether the fetal heart rate and fetal movement are abnormal. Doctors can determine the health status of the fetus in the womb according to the fetal heart rate monitor, and make timely and appropriate treatment if there is any abnormality. Fetal heart monitor can be used from 16 weeks of pregnancy to monitor the fetal heartbeat. Generally speaking, the normal use of fetal heart rate monitor is not affected, fetal heart rate monitor acoustic radiation dose is far below the safety index requirements, but the use of fetal heart rate monitor in small gestational weeks to listen to the fetal heart needs certain skills, pregnant women use at home by themselves, such as diagnosis of the fetal heart, remember not to be too alarmed.