Predicting the Likelihood of Live Birth for Elective Oocyte Cryopreservation: A Counseling Tool for Physicians and Patients

Embryo viability decreases as chromosomal abnormalities associated with advancing maternal age increase. Oocyte cryopreservation has increased in popularity as more women have elected to delay childbearing. Some practices offering this procedure suggest freezing between 10 and 20 oocytes, based on age. Questions regarding the optimal number of cryopreserved oocytes required per intended offspring remain unanswered. The purpose of this retrospective analysis was to create a counseling tool for women wishing to undergo oocyte cryopreservation. The projected fraction of euploid blastocysts, maternal age, and number of mature oocytes retrieved were used to predict the probability of having at least 1, 2, or 3 live births. This analysis included data from 520 first fresh autologous cycles using intracytoplasmic sperm injection occurring at the Center for Infertility and Reproductive Surgery at Brigham and Women's Hospital between January 2011 and March 2015. Analyses were limited to couples diagnosed with only male factor (n = 423) and/or tubal factor (n = 43) infertility who underwent intracytoplasmic sperm injection. Cycles in which egg donation was used were also included (n = 54). Cycles were excluded from this analysis in the case of known decreased ovarian reserve or if preimplantation genetic diagnosis/preimplantation genetic screening was used. Embryo and blastocysts were evaluated on days 3 and 5, respectively. Blastocyst morphology was evaluated based on the stage of development and the quality of the inner cell mass and trophectoderm. Importantly, this model assumed that approximately 60% of transferred euploid blastocysts would result in a live birth. This model also assumed a 95% and 85% survival of thawed mature oocytes for patients younger than 36 years (and egg donors) and older than 36 years, respectively. A total of 6415 oocytes were retrieved from the 520 cycles included in this analysis, and the average fertilization rate for this population was 73%. Equation 1 was developed using Poisson regression models for the male-factor and/or tubal-factor cycles. Equation 1 calculates the probability that one mature oocyte will develop into a viable blastocyst [p(blast)] as a function of patient age (years, y). Equation 2 uses a separate model to determine the probability that a single blastocyst would be euploid [p (euploid)] in combination with the regression from Equation 1. Equation 2 calculates the probability of having a live birth with a given number of mature oocytes. Equation 2 is p(livebirth) = 1 - [1 - 0.6p(euploid) x p(blast)]number of mature oocytes. This analysis has provided an evidence-basedmodel to determine the probability of having 1, 2, or 3 live births as a function of her age at egg retrieval and number of cryopreserved oocytes. This model is intended to assist women decision making surrounding elective fertility preservation.