The Shettles Method is a natural family planning technique, popularized in the 1970s, designed to help couples influence the sex of their baby. It outlines specific timing and environmental adjustments for intercourse based on a theoretical understanding of X and Y chromosome-carrying sperm characteristics. This article examines the method’s scientific concepts, recommendations, and evidence regarding its actual success rate.
The Biological Basis of Sperm Differentiation
The Shettles Method relies on purported differences between X-sperm (female offspring) and Y-sperm (male offspring). The theory suggests Y-sperm are smaller, faster, and more fragile, with a shorter lifespan. Conversely, X-sperm are thought to be larger, slower, and more resilient, surviving for a longer duration within the female reproductive tract.
The theory also incorporates environmental pH, claiming Y-sperm prefer and thrive in a more alkaline environment, while X-sperm are thought to be hardier and better able to survive in the typically more acidic conditions of the vagina. The method attempts to exploit the fact that the female reproductive tract naturally becomes more alkaline closer to ovulation. Recent scientific research, however, suggests that the only confirmed difference between X and Y sperm is their DNA content, challenging these assumptions.
Application and Proponent Claims of Success
The practical application of the Shettles Method centers on manipulating the timing of intercourse relative to ovulation to favor one type of sperm over the other.
Conceiving a Boy
To increase the chances of conceiving a boy, the method advises having intercourse as close as possible to the exact moment of ovulation. This timing favors the faster, shorter-lived Y-sperm. Deep penetration is recommended to deposit the sperm closer to the cervix, where the environment is naturally more alkaline and less hostile to the Y-sperm. The female partner is also encouraged to have an orgasm, as the resulting secretions are thought to temporarily increase alkalinity.
Conceiving a Girl
To maximize the probability of conceiving a girl, couples are instructed to have intercourse two to three days before the predicted day of ovulation. This timing allows the fragile Y-sperm to die off, leaving the durable X-sperm to survive until the egg is released. Shallow penetration is suggested to deposit sperm in the more acidic vaginal canal. Proponents have historically claimed high success rates, often citing figures ranging from 75% to 85% based on anecdotal data from their patients.
Independent Scientific Evaluation of Accuracy
Scientific studies have analyzed the efficacy of the Shettles Method by comparing its claimed success rates against actual observed outcomes. The natural probability of having a boy or a girl is approximately 50/50. Studies that have rigorously tracked the timing of intercourse relative to ovulation generally conclude that this factor has no significant influence on the sex of the baby.
Despite proponent claims of 85% success, independent surveys and research often find outcomes only marginally better than random chance. Large-scale analyses have shown that the method may only increase the probability of the desired sex to around 51% to 55%, which is not a statistically meaningful improvement over the natural odds. One study published in the New England Journal of Medicine concluded that the timing of sexual intercourse in relation to ovulation did not influence the sex of the baby. Furthermore, some research has even found results that contradict the Shettles hypothesis, showing that more female conceptions occurred when intercourse was closer to ovulation.