An old myth is that the woman decides the sex of her baby when she gets pregnant. Even today, some cultures still have this belief. So, what's the myth about this myth? When I was a child, I learned that it is the father that determines the sex of the baby. Of course, this is as big of a myth as believing the mother has control over this event.
The fact of the matter is that barring actual (and expensive) medical intervention, and for all practical purposes, the selection of a baby's sex is completely random. Neither the mother nor the father can make the selection through conscientious efforts. There are many different and often bizarre myths surrounding conception, as an article at babycenter.com covers.
Many different actions can be tried with to improve the chance of getting pregnant, but sex selection is still not directly in the hands of either parent. Granted, Y (male) sperm have been deemed weaker and can be more affected by a woman's pH balance more so than X (female) sperm, but more boys are born than girls on a world wide basis. Nature has already figured all this out for us, and if decision making has happened, it is a result of our species' evolution, and not preferences we conjure up in our own minds.