Maxis said that eating certain foods may increase the chances of having twins. Naturally, players everywhere tried this.

Some people have stated that if you feed your Sim cookies during the first trimester, you will raise your Sim's chances of twins to 68%. Evidence states that this is wrong.

Twins are determined at conception, not birth. (Gender, however, isn't.) Therefore, eating cookies in the first trimester isn't going to do a thing - your Sim is either pregnant with twins or not.

So, your Sims can eat all the cookies they want while in their first trimester, but it isn't going to make a difference.

Mac and Cheese is also a food rumored to increase the chances of twins. I can't say much about this food either way, since I haven't heard too much about it. (The lack of information may be an indicator to its effectiveness, on the other hand.)

Spaghetti, on the other hand, seems to be very effective. I've read several posts where people have had excellent success with the tomato-sauced pasta. Remember, though, your Sim would have to eat it before conceiving for it to work. It's not guaranteed to work, though - it's only supposed to increase the chances.

So, how do we know when twins are determined?

The game comes with two pregnant Sims - Brandi Broke of Pleasantview, and Pascal Curious of Strangetown. When these Sims give birth in the players' games, they always give birth to one baby, sometimes a boy, sometimes a girl, but never twins. If twins were determined at birth, Brandi and Pascal would have twins at least some of the time, but they never do!

Other rumored (and false) methods of aquiring twins: