Certain countries have a method of discerning the fertility of males and females. It’s a practice of maturity that the great wise men and women know. However, the only fertility is the one that comes from chastity and obedience to commandments, for closeness to God is closeness to life. And life is the source of all fertility and blessing.
The idea of there being some kind of practice aside from the commandments is just paganism, occultism, and trickery.
Therefore, the only method of discernment is whether a man or woman is close to God or not by his outward conduct and inner disposition and mind.
Virginity, not promiscuity, is in fact fertility - not for one, not only for two, but for thousands, simply by closeness, exposure, and loving interaction.
One saint can make fertile an entire people by his love, prayer, simple affection, and aroma, giving birth not only to children through chaste marriage but spiritual birth through prayer, speech, and example.
Only few know what it’s like to be the fertility of nations.