However, in recent years, some medical workers have put forward different views. For example, 1994, Dr. Kembel of Cary University in Canada studied some children with language development disorder, and thought that children's language development retardation was related to prenatal B-ultrasound diagnosis. During 1997, German geneticists believed that ultrasound was harmful to developing fetal cells, and heating was one of the causes of cell damage. Even if this view is established, it generally only affects the fetus within 3 months, because the fetus in the first trimester is delicate and vulnerable to external physical and chemical factors.
For the sake of prudence, if it is not necessary within 3 months, ultrasound examination can be omitted. At present, ultrasound is mainly used for examination in the third trimester of pregnancy, and most of them are used for prenatal diagnosis. It is generally used to distinguish whether the fetus is normal, whether there is too much amniotic fluid, whether there is a mole, whether the fetal position is normal, where the placenta is, whether it is a singleton or a twin, and whether it is a stillbirth or a live fetus. Ultrasound examination for pregnant women usually takes a short time, only a few minutes, and generally does not affect the fetus in the second and third trimester of pregnancy. From the perspective of eugenics, it is necessary to have an ultrasound examination during pregnancy.
Ultrasonic wave is a kind of vibration wave. The frequency of sound waves that can be heard by human ears is between16 and 20000 Hz; If the frequency of sound waves is above 20000 Hz, people can't hear it. This is called ultrasound. At present, the principle of ultrasonic flaw detector is based on the different densities of organs and tissues in human body. After ultrasound enters the human body, it can produce different reflection, refraction, absorption and attenuation, and the images of organs in the human body can be displayed on the B-ultrasound instrument, so B-ultrasound examination is a physical examination method. The dosage of ultrasound used by various B-ultrasound instruments at home and abroad for diagnosis has not been found to have adverse effects on the fetus and pregnant women. Because it is safe, simple and non-invasive, it can be checked many times in the third trimester.