How much does IVF increase a woman's odds of having twins or multiple babies at once?

According to this article I read, "If you have in vitro fertilization (IVF), your chances of having more than one child vary depending on your age, how many embryos are placed in your uterus, and other factors." Read more about it here: http://www.babycenter.com/0_your-likelihood-of-having-twins-or-more_3575.bc