Probabilities for singleton and multiple pregnancies after in vitro fertilization

Objective: To help physicians provide risk estimates for specific pregnancy outcomes. Design: Computation of exact binomial probabilities for singleton and multiple pregnancies as a function of two inputs: the number of embryos transferred and the implantation rate. Inputs were varied over the range of values reported in the literature. Main Outcome Measure(s): Probabilities for a singleton pregnancy (P-one), a multiple pregnancy (P-mult), and no pregnancy (P-none) after one IVF cycle. Result(s): Given a 30% implantation rate and three embryos transferred, P-one = .44, P-mult = .22, and P-none = .34. Although further increasing the number of embryos transferred increases the chance of pregnancy, it also raises the probability of a multiple pregnancy and lowers the chance of a singleton pregnancy. Although varying the implantation rate changes the specific probability estimates, the same trade-off persists. Conclusion(s): Those who consider an IVF "success" to be a singleton pregnancy should be attentive to the number of embryos transferred. Infertility therapy may be one area in medicine where more is not necessarily better. (Fertil Steril(R) 1998;70:478-81.