Similar to the above, I heard this some years ago:
Girl sperm swim slowly but can swim for a long time before dying out.
Boy sperm swim fast but die out quickly.
So .. if you want a girl, she'll want to be upright afterward ... the boy sperm will swim against gravity and die quickly .. the girl sperm will also swim against gravity but will have a better chance of making it as they can swim longer before dying.
If you want a boy, do the opposite ... ie., she should be upside-down so that the quick-swimming boy sperms go with gravity and win the race.
Good luck ...
