I have heard that as well... but wouldnt doing it every day mean that the spermies could really build up and the chances are even higher?

I posted a thread about BDing while Oing and a couple of the ladies said that the reason some dont BD on O is for gender swaying? Male swimmers are faster but female swimmers live longer, something like that! LOL I think that might be the reason for only doing it every second night as well, but not entirely sure!