Since the fetal heart is far away from the skin surface of the pregnant woman, the fetal heart may be faint when listening to the fetal heart without couplant, and the doctor needs to look carefully to the position of the fetal back to hear it clearly. Without the use of couplers, the heart rate heard may be the heart rate of the pregnant woman, which may make it more difficult to detect and lead to inaccurate fetal heart values. The main function of medical couplant is to increase the lubricity of the probe, which can make the probe come into close contact with the body and avoid the effect of gas and the natural depression of the body surface on the examination effect, thus increasing the sound transmission and facilitating better hearing of the fetal heart. Coupling agent is a medical product, non-toxic and harmless to human body, no allergic reaction, and no radiation, so there is no harm to pregnant women and fetus, just wipe the coupling agent on the examination site with tissue or towel after the examination.