The Shettles method is a technique which supposedly allows parents to influence the sex of their baby by timing conception and using specific sexual positions. There is substantial debate over this method. Adherents claim that it is highly successful and may point to their own children as evidence, but numerous scientific studies have shown that the Shettles method and other tricks which are designed to influence sex actually have no effect. In fact, higher rates of infertility have been observed in such studies, which may be due to a number of factors beyond techniques like the Shettles method.
This technique, developed in the 1960s by Dr. Landrum B. Shettles, operates on the theory that sperm have different characteristics depending on whether they are carrying an X chromosome or a Y chromosome. Dr. Shettles believed that sperm carrying an X chromosome were larger, slower, and more hardy, while Y chromosome sperm were faster, smaller, and more delicate. In particular, Y chromosome sperm were susceptible to the normally acidic environment of the vagina.
Using this premise, Dr. Shettles proposed a method for timing conception which would allow parents to promote either X or Y sperm in order to get a girl or a boy. For a girl, conception would take place before and after ovulation, with shallow penetration to give the slower sperm more time to beat out the faster sperm. For a boy, conception would take place as close to ovulation as possible, with deep penetration to give the supposedly fast male sperm a head start. Dr. Shettles also claimed that if the female partner had an orgasm, it would make the vagina more alkaline, increasing the chance of survival for male sperm.
The Shettles method for sex selection does not appear very effective in scientific studies; statistically, there are slightly more girls than boys, for a variety of reasons, and attempts to influence sex during conception do not seem to work. Numerous cultures have attempted to find a foolproof way of selecting sex ahead of time, and thus far the best method seems to be using assisted reproductive technology to choose an embryo, with sex being one characteristic which can be easily tested for before implantation.
It is unclear whether things like the Shettles method increase infertility, or couples with a natural predisposition to infertility are more likely to try this method. Some researchers have suggested that the stress which surrounds sex and conception, including careful monitoring of ovulation and restrictions on sexual activity, may contribute to difficulties with conception when trying the Shettles method.