Ultrasound examination is a physical examination method that closely combines the physical properties of ultrasound waves (such as directionality, reflection, attenuation, resolution, and penetrability) with the acoustic characteristics of human tissue structures. Ultrasound consists of sound waves with very high vibration frequencies, exceeding the upper limit of human hearing. By utilizing its physical properties, it emits and receives echo signals into human organs and tissues, thus aiding in diagnosis and treatment. Sound waves are a physical factor, a form of energy, and there is a safe dosage issue. Whether ultrasound is harmful or harmless to the human body or fetus depends on the ultrasound dosage, also called the threshold safe dose. That is, when the ultrasound dose used is below this value, it is harmless; conversely, when it exceeds this value, it may produce harmful effects or damage. Fetal heart rate monitors also use the ultrasound principle, but their sound intensity is much lower than that of ordinary B-ultrasound equipment. The international ultrasound medical community has an ALARA principle, which is “to obtain the required information with the lowest possible sound output.” Ultrasound diagnosis is irreplaceable in prenatal care and has long been considered a simple, reliable, painless, non-invasive, radiation-free, and safe examination and diagnostic method in the field of obstetrics. For pregnant women after 28 weeks of gestation, the fetus has fully differentiated, and the monitoring time and frequency can be extended.