LETTER TO THE EDITOR REPLY OF THE AUTHORS: We read with interest the letter detailing incorporation of the aneuploidy rate at any given maternal age into a broader model predicting the mean number of vitrified oocytes required to attain a live birth. In our experience, this is the single most common question that arises when counseling women about fertility preservation. The simple but elegant formula detailed by Nejat et al. incorporates several critical factors including oocyte survival after warming, fertilization, and development rates (number of oocytes required to attain a blastocyst), the age-specific aneuploidy rate as detailed in our recent publication, and the sustained implantation rates attained with euploid blastocysts. In considering this formula, we would voice only a single caution. The equation considers the means of each factor included in the formula. It is not obligate that they would all be independent and that the arithmetic result would actually equate to the overall mean number of oocytes required. Even if the mean were accurately calculated, a substantial portion (i.e., those above the mean) would actually require a larger number of oocytes. At a minimum, it might be more useful to incorporate the 95th percentiles of the blastulation and implantation rates into the model. The same interesting principle detailed by Nejat et al. might also be applied to the infertile population undergoing IVF. Similar logic might yield a mathematic algorithm applicable to patients interested in both conceiving now and extending their family in the future. In this case, rather than calculating number of oocytes required for a live birth,

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one might estimate the number of euploid blastocysts that are needed. Patients may then pursue embryo banking during a time when their reproductive efficiency is at its maximum— knowing it will only decline with age. They may then defer transfer and accrue euploid blastocysts until they are comfortable with the likelihood of realizing their full family planning goals. Such a strategy would allow them to space their family at intervals of their choice rather than being compelled to pursue pregnancies as quickly as possible. As treatment algorithms continue to become more successful and access to high quality fertility preservation increases, the ability to prognosticate outcomes has improved. There is no doubt that algorithms, such as the one described, will be validated and then applied to assure that the most accurate counseling empowers couples to plan their reproductive futures on their own terms. Jason M. Franasiak, M.D. Eric J. Forman, M.D. Richard T. Scott Jr., M.D., A.L.D./H.C.L.D. Division of Reproductive Endocrinology, Department of Obstetrics Gynecology and Reproductive Science, Robert Wood Johnson Medical School, Rutgers, Basking Ridge, New Jersey April 22, 2014 http://dx.doi.org/10.1016/j.fertnstert.2014.05.009

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