A 4D ultrasound can reveal the sex of the fetus, mainly through the fetus’ genitals. Generally around 12 weeks ultrasound can initially identify the gender of the fetus. The 4D ultrasound examination is usually conducted at 20 to 24 weeks of pregnancy, at which stage the genitals of the fetus have been fully developed, so the ultrasound can be used to determine the gender of the fetus from the genitals point of view. If it is a girl, no light translucent shadow will be seen between the legs of the fetus, on the contrary, if it is a boy, there will be light transparent shadow between the legs of the fetus. 4D ultrasound examination is mainly used to identify whether the fetus has malformation of organs, such as the width of the ventricles, the structure of the heart, etc. It is not used to identify the sex of the fetus. In addition, the relevant laws of China stipulate that during prenatal examination, it is not permitted to carry out the examination of the sex of the fetus unless it is to determine the incidence of genetic diseases.