A girl diagnosed by ultrasound is generally unlikely to give birth to a boy, unless the doctor makes an error of observation during the examination, but it is not currently permitted to carry out sex determination in advance without medical indication. Ultrasound diagnosis of the sex of the fetus is mainly through imaging to directly observe the appearance of the genitals of the fetus, and can effectively determine whether it is a girl or a boy. The complete external genitalia can usually be observed at around 16 weeks of fetal life. Since the gender of the fetus is influenced by congenital genetic factors, there will be no further changes after the initial determination of gender. However, the position and activity level of the fetus during the imaging examination may cause the doctor to make an observation error, which will affect the final determination of the sex. However, it is not permitted to determine the sex of the fetus in advance during routine checkups and for healthy pregnant women. It is recommended that pregnant women should not pay too much attention to the sex of the fetus during the examination, and that they should take timely nutritional supplements and take good care of themselves during pregnancy.