Success varies with many factors. The age of the woman is the most important factor, when women are using their own eggs. Success rates decline as women age, specifically after the mid-30’s. Part of this decline is due to a lower chance of getting pregnant from ART, and part is due to a higher risk of miscarriage with increasing age, especially over age 40.
Success rates vary with the number of embryos transferred. However, transferring more and more embryos at one time does not increase the chance of live birth significantly, but may only increase the risk of a multiple pregnancy, and its associated risks. The impact of the number of embryos that are transferred also varies with the age of the woman.
SART, in conjunction with, The American Society for Reproductive Medicine (ASRM), has published guidelines for the recommended number of embryos to transfer (add to link). These guidelines are based on SART-sponsored research which continually evaluates success rates around the country. This helps to determine the optimal number of embryos to transfer, based on specific patient characteristics, like age and history of prior IVF. Patients may require several cycles of treatment to have a baby. Success rates remain fairly constant over several cycles, but may vary greatly between individuals.
It is important to note that patient characteristics vary among programs; therefore, success rates should not be used to compare treatment centers.