Figure 2. Logic for predicting outcomes of a double embryo transfer incorporating a universal factors fraction and live birth rates for embryo 1 and embryo 2. The universal factors fraction is a fraction from 0 (never favorable) to 1 (always favorable). The probability of each outcome is equal to the product of the terms next to the corresponding arrows above and the corresponding terms on the perimeter of the square. For example, the probability of twins is UNI × × . This same logic can be applied to transfer of more than two embryos. UNI = universal factors fraction; LBRe1 = live birth rate for embryo 1; LBR_e2 = live birth rate for embryo 2.