Ultrasound can initially determine the sex of the baby at around 20 weeks, but can only be used to determine the sex of the baby when medically necessary, and non-medically necessary sex determination is illegal. At around 12 weeks, the difference between the genders becomes apparent, and at 16 weeks, the sex of the fetus can be determined through the external genitalia. 20 weeks will be required for ordinary ultrasound, and there are earlier methods of identifying the sex of the fetus, most of which are invasive. Various means of sex determination are available for prenatal diagnosis of hereditary diseases. A family history of sex chromosome disorders can be used to reduce the incidence of these disorders with a doctor’s certificate. For example, hemophilia, pseudohypertrophic progressive muscular dystrophy, red-green color blindness and other X-chromosome genetic diseases have a high incidence in boys, and in view of the dangers of the diseases, pre-implantation genetic diagnosis techniques can be used to select female embryos for implantation into the uterus. Our law stipulates that non-medical need for fetal sex identification is illegal, and artificial intervention in the sex of infants is illegal.