My MIL swears by this theory that girl swimmers are slower and live longer and boy swimmers are faster and die faster. Therefore, on O day and after is the best chance if having a boy and O minus 1 and before is the greatest chance of having a girl. I don't know if I buy into this. I don't know when I conceived DS we DTD 5 out of 7 days that week. I wanted to test this theory next year, but got pg a year sooner. Anyone firmly believe in this? Just out of curiosity.