The sex of a fetus is determined by the sex chromosomes provided by both parents. The sex of the fetus is determined from the time the fertilized egg is formed. There are two sex chromosomes, one from the mother and one from the father. The mother can only provide the X chromosome, while the father can provide either the X or Y chromosome. If the mother’s X chromosome combines with the father’s X chromosome, it is a girl; if the mother’s X chromosome combines with the father’s Y chromosome, it is a boy. Usually the chance of X chromosome and Y chromosome combination is random, so the chance of having a boy and a girl is equal, and any so-called special method of determining the birth of a boy or a girl is unreliable. In the clinic, if the patient has a sex chromosome genetic disease, the eugenic guidance can be carried out by a professional physician.