I also think its easier to gender sway in favour of a boy than a girl. It seems from my general observation that even with unplanned babies; there just seems to be a knack of getting pregnant right on ovulation. Boy sperm swim faster but die quicker so it stands to reason that that side of gender swaying would give you a huge advantage. On the other hand, girl sperm live longer but swim slower. Which makes it difficult because you can only pinpoint ovulation to within a 24hr time frame, sometimes even longer so trying to keep those quick swimming xy's from getting the egg is a mean feat genetically. If your off with your timing the swaying goes out the window. I also think its difficult to know just how long your partners sperm actually lasts for. I know they say its 3-5 days but I would think it varies individually. I have a theory that my husbands sperm is predominately xy and that they dont live very long which could be why a) it took us so long to conceive Ds1 and b) why even though #1 and #3 should technically be girls they arent.