The birth of a boy or girl is determined by the Y chromosome of the sex chromosomes. Sex chromosomes determine gender. Males and females usually have 23 pairs of chromosomes, 22 pairs of autosomes and one pair of sex chromosomes, the female sex chromosomes are usually XX and the male sex chromosomes are usually XY. If the Y chromosome of the male combines with the X chromosome of the female, a boy is formed. If the male Y chromosome combines with the female X chromosome, a boy is born. If the male X chromosome combines with the female X chromosome, a girl is born. The sex of the fetus is usually determined at the moment of fertilization. The birth of a boy or a girl is a social and natural developmental process that maintains a balanced ratio of males to females. In our country, any non-medical indication of the sex of the foetus is prohibited, with the exception of sex chromosome-related genetic disorders that require medical indication for sex determination.