To have a baby girl the man's X chromosomes must fuse with the woman's X chromosomes to form the XX gene combination. To have sexual intercourse in any day of the 3 days before the ovulation day will bring about the XX gene combination.the reason is that the Y chromosomes does not stay beyond 24 hours after ejaculation;sexual intercourse in any of the 3 days to the ovulation day is a deliberate action to allow the Y Chromosomes to die before the ovulation day.When that happened the X chromosomes which moves slowly and has the ability to stay up to 3 days,can have the chance to fuse with X chromosomes of the woman;when the egg is eventually released.