As boy sperms live shorter but swim faster they reach an egg that has already been released before the girl sperms. Therefore if you want a boy you need to have sex on the day of ovulation and if you want a girl you have sex 1-2 days before ovulation. The girls will get to the destination after the boys but the boy sperm will die before the egg is released. You need to know your cycle 100% for this system to work otherwise you cannot guarantee anything. I wanted 2 boys and tried this method and got boys both times. Who knows, but it worked for me, worth a try we thought. Good luck.
Michelle, 2 boys, 2 3/4 and 17mths