[wai-ming]

Scientists believe that the reason is that boy babies tended to be bigger which make them harder for smaller women to give birth to.

Very misleading in this context. This would make it an issue of "delivery" not "conception."

[billorites]

This would make it an issue of "delivery" not "conception."

There's lots of evidence that suggests males fetuses are less viable than female. The rate of spontaneous miscarriages is higher among male fetuses for reasons that aren't fully understood.