The wish to choose baby gender is very strong. It goes back hundreds and thousands of years. In fact, it has probably been around for as long as humans have existed.
Originally, people in most cultures believed that the sex of the child was determined in the mother’s body. That was a natural assumption before science began to investigate the role of men and their sperm in the conception of babies. Women were held responsible for the children that they produced.
This meant that if a woman kept giving birth to daughters when her husband wanted a son, she would be blamed and might be cast out or perhaps even murdered so that he could take another wife. Not surprisingly, she would go to the local wise woman for advice on how to choose baby gender. Every culture had its own superstitions about what a woman should eat, wear or do to increase her chances of conceiving a boy or girl.
Of course all this was pointless because the sex of a child is determined by the sperm, which is provided by the father. We now know that we have two sex chromosomes: XX for women and XY for men. When a baby is conceived, it receives one from each parent. A woman always contributes an X because that is all she has. The man will have a mixture of sperm, some carrying a copy of his X chromosome and some carrying the Y. If one of his X chromosomes reaches the egg and fertilizes it, the baby will be female. If it is a Y, the baby will be male.
In rare cases, a child can be born with extra chromosome, resulting in what is called XXY or Klinefelter syndrome. This happens in one or two births per thousand. The child is still a boy, because he has received a Y chromosome from his father, but he will have less testosterone than other boys and may be infertile. The extra X chromosome is the result of a fault in cell division soon after conception.
It is not known for sure why some men seem to have children that are all the same gender. But if we assume that the odds of having a boy are 50%, then statistically, in a sample of 100 families who had 4 children, in 6 of those families all 4 children would be the same sex by pure chance. So it does not necessarily mean that the man will never have a child of the other sex.
There are several methods now for choosing the sex of a baby that are much more reliable than the old superstitions. One well-known method relies on timing: couples wanting a boy should have intercourse at the time of ovulation, couples wanting a girl should try a few days earlier.
It is also now possible to sort sperm so that those carrying the X chromosome are separated from those carrying the Y chromosome. Sperm of the chosen gender can then be introduced to the woman’s body by intra uterine insemination. This is an expensive procedure but it may be worthwhile if you very much want to choose baby gender.