I found this info on a website:
What are the chances of conceiving twins on soy isoflavones?
There is limited data available for the use of soy isoflavones to treat fertility, however it does look somewhat promising. The chances of conceiving twins may not be as high as the chances of conceiving twins on clomid, however, they are higher than what they would be otherwise.
Also something to think about:
Ironically clomid will NOT increase your chances of multiples IF you ovulate ON YOUR OWN. In fact it will hinder you as it drys up the valuable cervical fluid needed to help the swimmers. IT also thins your uterine lining, making it inhospitable for the egg. Many gals
Good, That is help.