The Shettles Method is a child conception idea that is reputed to help determine a baby's sex. It was developed by Landrum B. Shettles in the 1960s and was publicized in the book How to Choose the Sex of Your Baby, coauthored by Shettles and David Rorvik. The book was first published in 1971 and has been in print in various editions ever since.
By following the various methods outlined in the book, it is proposed that a couple can affect the probability of having a boy or a girl. Proponents claim between 75 and 90 percent effectiveness, but experts do not agree that the method works; for example, the 1995 article 'Timing of Sexual Intercourse in Relation to Ovulation—Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby', in the New England Journal of Medicine concludes that "for practical purposes, the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby."[1]
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According to the theory, male (Y) sperm are faster but more fragile than female (X) sperm. Further, acidic environments harm Y sperm, according to the theory, making conception of a girl more likely[2]. The Shettles method aims to exploit these two factors.
The Shettles method differs from the Ericsson method, in which the semen is deposited outside the woman and time is given for the fast/slow swimmers to separate before artificial insemination takes place.
In order to have a boy insemination should occur as close as possible to the moment of ovulation so that the faster, Y-sperm arrive first and achieve conception, according to the theory. When seeking a girl insemination the couple should seek to have sex 2½ to 3 days before ovulation.
Shallow penetration coupled with the sperm deposited close to the entrance favors female conception because the area is more acidic, which inhibits the weaker Y sperm, according to the theory. To allow the Y sperm to reach the egg first (which supposedly moves at a faster rate), deeper penetration should be sought, to deposit the sperm at the least acidic area near the uterus opening.
Female Orgasm favors male sperm because they make the vaginal environment more alkaline.