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. Concept According to the hypothesis, 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 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. Timing of Intercourse 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 hypothesis. When seeking a girl, the couple should have sex 2½ to 3 days before ovulation. Sexual Position 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 hypothesis. To allow the Y sperm, which supposedly moves faster, to reach the egg first, use deeper penetration to deposit the sperm at the least acidic area near the uterus opening. Intercourse should occur from 5 am and continue every 2 hours during the ovulation period. Eggs are more likely to be fertilized before 7 am known as "the peak period". Effectiveness Proponents claim between 75 and 90 percent effectiveness for the method. May 19, 1998, Landrum B. Shettles, M.D., PhD dictated to his daughter, Lana B. Shettles-Callahan, an email reply to Professor Hunt concerning the presentation of choosing the sex of your baby with the following statement: “David M. Rorvik and I published in 1971 How to Choose Your Baby's Sex with revised editions in 1977, 1984, 1989, and 1997 in seventeen languages with worldwide distribution. To date, over one million copies have been sold and over 25,000 answers to the questions 'what you want'