The chances of the first child being a boy and the second child being a girl are about 50%, which is not directly related to the sex of the first child. There are 46 human chromosomes, 22 pairs of which are shared by couples and are called autosomes. The chromosomes that are directly related to gender are the sex chromosomes, which are XY for males and XX for females. The birth of a boy or girl is determined by the male’s sperm. Fertilization occurs through the combination of haploid cells from both partners; the woman will provide an egg with an X chromosome, and the man will provide two types of sperm, an X chromosome and a Y chromosome. The combination of the egg and the X sperm will develop into a female and the combination of the egg and the Y sperm will develop into a male. The chances of having a boy in the first pregnancy and a girl in the second pregnancy are about 50%. It is recommended that couples follow the natural state, live a reasonable diet, do not stay up late, and enhance exercise.