I don't know of any point in history when this wasn't true (and it disappoints me).
For many reasons (most dated, all stupid) male is the preferred gender for expecting parents.
Not to says all, many or most parents want boys and don't want girls. I think MOST parents are neutral, they may lean one way or another but they'll be happy with either.
BUT of the ones who are actively hoping for one gender over the other to the point that they will be legitimately upset if they don't get their preferred gender... it is always wanting a boy.
I have NEVER seen parents get upset about getting a boy, the way some parents get about getting a girl... and it's disgusting.
Starfire: "They are too numerous to fight. What shall we do?"
Robin: "Fight anyway!" (pb)