Actually it is sort of a level playing field, they have done studies that a sperm have different advantages based on whether they are X or Y. Y sperm tend to swim faster than X sperm....so if the egg is in the already released odds are it will be a boy. But the X sperm live longer so if the egg has not been released the odds are it will be a girl.
My information from maybe thirty years ago is that the playing field is not entirely equal... indeed, there are more baby boys born than girls...I think I recall something like 104 boys to each 100 girls?
But the figures even out quite soon, until old age women outnumber men...
my2cents 