Don’t Have an Orgasm
According to the Shettles method, the timing of conception is the biggest factor in determining the sex of your baby. Along with some other medical experts, Shettles claims that Y-chromosome sperm (boys) are faster swimmers than X-chromosome sperm (girls). However, girl sperm are thought to be more "resilient," surviving longer in the reproductive tract than boy sperm.
Based on this theory, you're more likely to conceive a girl if you have intercourse every day for two to four days before ovulating and then abstain from sex one to two days before ovulation and a few more days after ovulation. The premise is that by the time you ovulate, all of the male sperm have died off leaving only female sperm to fertilize the egg. Conversely, if you have intercourse on the day you ovulate, the faster-swimming male sperm may beat the girls to the egg. This approach means you'll have to know your cycle. and do some very careful calendar watching, or take an ovulation test to determine precisely when you're ovulating.
Another theory claims that girl-producing sperm prefer, or can at least tolerate, warmer temperatures. If you buy into this concept, you should encourage your partner to take a hot bath before intercourse if you want a baby girl.
Whether this works or not, don't overdo it. General advice for increased fertility is to keep those guys on the cooler side. So frequent hot-tubbing or overly brief briefs may have a long term deleterious effect. Overall sperm count changes over about two months.
The Shettles method also says that a woman's orgasm plays a role in determining the sex of the baby. The theory is that when a woman has an orgasm, her body releases a substance that increases alkaline levels. Because an environment high in alkaline favors boys, Shettles says a woman should not have an orgasm during intercourse if she wants a girl.
This would potentially be at odds with the advice of some experienced mothers: that doing the deed quickly and without ceremony is the way to get a boy!