http://www.childbirth.org/articles/sex.html

(2) The pH of the women's tract is also very important. A more acidic environment favors girls, since it will kill the weaker y-sperms first, leaving a greater quantity of x-sperms available to fertilize the egg. On the other hand, a more alkaline environment favors boys. Shettles recommends a douche of water and vinegar (acid) immediately before intercourse to favor a girl; a douche of water and baking soda (alkaline) will help for a boy.

(Don't try this without reading Shettles! You have to dilute the douches properly, according to his formula, or they won't help and might hurt you.)

Note: Some women are naturally very acidic and have a hard time conceiving boys.

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itt vannak egyéb trukkök is, pozíció, kávéivás, stb :D