Trying for Twins

Have any of you used natural methods to "try" for twins and it work? Like... eating lots of yams and things like that? I know this sounds so stupid, but twins do not run in my family, and I'm a 34 year old with a heart condition and I've always wanted 4 kids, but the cardiologist says no way to 4 pregnancies. (I have a 20 month old and the birth did not go as planned to say the least).