The book "sexual Odds" also goes on alot about how female organsm can affect the sex you have, as when we orgasm the cervix makes a sucking action...

Theory behind it is (and I'm remembering it very vaguely so it may not make sense!), boys swim faster... if you orgasm before you man does all your reproductive organs are relaxed and the boys are able to casually swim up there before the girls even have a chance... if you orgasm after your man, the girls get a bit of a helping hand in being sucked up by your cervix and pushed through with the contractions of the orgasm (in my mind I think this would just make the boys super fast... but apprently not!)

If it's any consolation, I always orgasm before DH and have been pregnant with both boys. But anyway... if you can find the book it's a good read