There are four basic provisions of the O+12 Method:
- Determine ovulation using ovulation prediction
- Abstain from ejaculation prior to sex to conceive
- Have sex once, twelve hours after ovulation
- No unprotected sex until you are no longer fertile
A non-scientific study done by the creator found that out of 41 attempts, found that there was a 90% success rate for conceiving a girl. Online surveys do not back up the 90% success rate, though obviously there are successes.
If you are really interested in trying to have a girl and you do not want to do medical methods of gender selection, you might also try other methods that go along with the O+12 method. Examples might be diet, lifestyle and vitamins.
One issue might be the timing of sex. Once ovulation has passed, the risk of not conceiving at all is greater. If you find that you are having trouble conceiving while using this method, you may want to reconsider what you are doing and seek the advice of a fertility specialist.
A prospective study of the preselection of the sex of offspring by timing intercourse relative to ovulation. France JT, Graham FM, Gosling L, Hair PI. Fertil Steril. 1984 Jun;41(6):894-900.