Every parent is familiar fuss about the sex of the child: someone feels just curious, having no preference, while for some it is comparable to the difference between life and death. Child's sex is determined at the time fertilization and depends on whether the sperm fertilize the egg: supporting X-or Y-chromosome. 'Ladies' (X) sperm are slightly different from the 'male' (Y). They have a relatively large size, 'float' slower more resistant to neblagopryatnym factors and live a little longer. Since the discovery of these differences in the behavior of 'female' and 'male' sperm have begun attempts to use them for the couples. In the 60's years published an article by Dr. Shettlsa about the invention of the method, which, as stated in 75 – 90% guaranteed to conceiving a child the right floor. The method was based on the time from intercourse prior to ovulation, depth of insertion of the penis into the vagina and the presence of orgasm in women.

To conceive a girl proposed to have sexual intercourse not later than 2 – 3 days before the expected ovulation, use a shallow penetration (penetration), and Women recommended to refrain from orgasm, because it changes the environment vagina to the alkaline side. When using these techniques was expected that by the time of ovulation, less stable 'male' sperm will die in the acidic vaginal environment, and will remain, mostly, 'female'. To conceive a boy, it was recommended to have intercourse before ovulation, using positions for deep penetration, and a woman have an orgasm.