There is no way to control the birth of a baby. The birth of twins is actually heterozygous, requiring a woman to discharge two eggs during ovulation, and also need to be combined with the X chromosome and Y chromosome respectively, which is a natural process of conception, is a random event, and there is no way to artificially control and improve the normal situation. Unless one chooses to undergo IVF, it is possible to screen the sex and number of fetuses, but this is generally not recommended, and selection of the sex of the fetus is currently strictly prohibited. In addition, pregnancy is a natural process, there is no need to excessive pursuit of the dragon and phoenix child, should be more concerned about the health of the fetus.