The vagina is highly acidic at the end of the ovulation cycle. The male sperm is smaller than the female sperm. The slower swimming male sperm, dies in the highly acid environment. The Roman Catholic who practice only waiting to the end of the ovulation cycle need to know, no matter how many rosaries they pray, they're never going to have a male offspring doing it his way. That's why a massive bunch of female births occur in Catholic families. Mostst of them. I knew had 5 daughters, blamed God because they were given only daughters as children.