A prenatal 4D ultrasound can observe the growth and development of the fetus and rule out fetal abnormalities. Of course, the external genitalia of the fetus, especially those of boys, can be clearly displayed in 4D ultrasound, which means that it is easy to distinguish between boys and girls. However, doctors cannot describe what they see in the ultrasound report regarding the sex of the fetus, because there are clear regulations in the country regarding the examination of the sex of the fetus, and no medical unit or individual can do fetal sex identification, otherwise it is an illegal act.