4D ultrasound is the most advanced color ultrasound equipment in the world, which can observe the growth and development of the fetus in the womb in all aspects and can detect any congenital physical malformation and congenital heart disease in time. Generally, it is possible to distinguish male from female between 20-28 weeks of pregnancy, and can be judged by the development of reproductive organs. However, China clearly stipulates that non-medically necessary fetal sex determination and sex-selective artificial pregnancy termination are prohibited. Therefore, during the examination, in order to avoid revealing the sex of the fetus, doctors will actively avoid the sex characteristics of the fetus, and also in the post-production of the CD, the parts that may reveal the sex of the baby will be processed. However, some hereditary diseases are closely related to gender, and there are various forms of transmission from mother to son only and not to daughter, and from father to daughter only and not to son. The purpose of predicting the sex of the fetus for such mothers-to-be is to avoid the continuation of genetic diseases and to ensure eugenics. It is recommended that if there are no congenital physical defects and other problems, parents should be more concerned about the health and normal development of the fetus than the sex. Usually, they should keep their mood relaxed and do regular pregnancy tests.