The 4D ultrasound images are clearer and allow for real-time dynamic observation of fetal movements, behaviors, and expressions. The external genitalia of the fetus begin to differentiate at 8-11 weeks of gestation, and in the case of a boy, the genital nodes evolve into a penis. In males, the testes begin to descend into the scrotum at 25 weeks, and the form of the external genitalia can be revealed in mid- to late-gestation when the fetus is lined with amniotic fluid between the thighs. Ultrasound can identify the sex of the fetus, and the accuracy can be as high as 90% or more. Boys can show the structure of the scrotum, testicles, penis, fetal gender four-dimensional color ultrasound is strictly prohibited to identify, in violation of national laws and regulations.