Dr. Landrum B. Shettles book, How to Choose the Sex of Your Baby (1970, co-author, David M. Rorvik), has for years been the sex selection ‘bible’ for many. The book has been revised numerous times, most recently in 2006, several years after Shettles’s death.
The key to the Shettles method is calculating the time of the woman’s ovulation — and then attempting conception during or before ovulation — to conceive a desired boy or girl baby. Shettles found that Y-bearing (male) sperm swim faster but don’t live as long as the bigger, hardier X-bearing (female) sperm. This method also assumes that the vaginal environment is acidic most of the time, but becomes slightly more alkaline close to ovulation, favoring boy conceptions (Y-bearing sperm).
According to the Shettles Method:
- To conceive a boy baby, a couple should have sex on the day of ovulation or 1 day before;
- For a girl baby, couples should have intercourse 2 or 3 days before ovulation.
To use the Shettles method, women must track their cycles with a Basil thermometer to pinpoint their normal time of ovulation (or use other methods.)
Shettles also suggests using acidic douches, as a supplement to increase the chance of conceiving a girl. Another recommendation: females should orgasm during intercourse, which supposedly alkalinizes the vaginal environment, favoring boy babies. For baby girl attempts, the woman should forego orgasm.
Shettles’s method claims an 80% success rate for boy conceptions and about 74% for girl conceptions. However, the American Journal of Obstetrics and Gynecology published a study that failed to confirm Shettles’s theory on intercourse at ovulation would result in more male offspring. The New England Journal of Medicine reported similar findings. Shettles’s claim that Y-bearing sperm swim faster than X-chromosome-bearing sperm has also been refuted.
 R. H. Gray, “Natural Family Planning and Sex Selection: Fact or Fiction?” American Journal of Obstetrics and Gynecology 165 (1991): 1982-84.
 V. A. J. Wilcox, C. R. Weinberg, and D. D. Baird, “Timing of Sexual Intercourse in Relation to Ovulation: Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby,” New England Journal of Medicine 333 (1995): 1517–21.