I believe in swaying. I've even been doing gender predictions based on swaying information to guess the genders on my DDC. So far I have gotten 8/9 guesses correct. I notice if you put together a group of women who sway based on information based from studies, they get the gender they want more than 50% of the time, which tells me something. It's not 100%, but it does increase your odds.
Even smoking can sway!
Smoking (sways a little if man smokes, sways a lot if woman smokes)