While an opening day invited presentation concluded that outcome was improved with a greater number of oocytes cryopreserved, Ana Cobo warned that success rates would also depend on the patient population and diagnostic background.
The take-home message from Ana Cobo’s opening day presentation on oocyte cryopreservation was ‘the more the better’. However, the Director of the Cryobiology Unit in IVIRMA Valencia also emphasised the importance of managing fertility patient expectations, with the warning that oocyte cryopreservation is not a ’one shoe fits all’ service, with varying outcomes depending on the patient population and diagnosis.
With significant demands for oocyte cryopreservation, ESHRE’s EIM Consortium reported a 62% increase in frozen oocyte replacement cycles between 2008 and 2013. Similarly, HFEA data in the UK reported a 240% increase between 2013 and 2018, while Spanish National Register reported that more 50% of donor oocyte cycles were now with vitrified oocytes. This worldwide increasing demand for egg freezing was also described as ‘exponential’ in an opening keynote lecture by Antonio Pellicer.
However, this significant demand for oocyte preservation services must be coupled with the importance on managing patient expectations, said Cobo, and presenting realistic survival and outcome figures tailored to the population cohort. Indeed, the population cohorts now turning to oocyte cryopreservation services reach beyond those simply looking to delay childbearing, but must now also include several pathological reasons for egg freezing; oncology-fertility preservation, endometriosis, natural depletion of ovarian reserve and poor responders.
Advances in vitrification have reduced the vulnerability of the eggs to cryoinjury, with Alpha and Vienna consensus expecting oocyte survival rates ranging from 80-99%.(1,2) This relatively high benchmark can, however, generate a false sense of security. Cobo thus presented data from Forman et al showing a 15% higher blastocyst formation from fresh oocytes than from vitrified.(3) Embryo development, encompassing fertilisation, cleavage and utilisation rates, was also higher in fresh oocytes than in vitrified.
Recent studies by Cobo’s IVI group have suggested significant differences in survival and clinical outcomes after oocyte vitrification depending on patient pathology and clinical indication. Matching for age groups, oocyte survival rates differed when comparing social egg freezing populations (elective fertility preservation (91.4%)) compared with those with pathological diagnosis such as cancer (81.2%). A 26% difference in clinical LBR was also observed comparing these two different oocyte preservation populations.
Similar differences in oocyte survival rate (6%), implantation rate (16%), clinical pregnancy rates (16.7%) and LBR (6.9%) were observed when comparing endometriosis patient populations with social egg freezing patients.(4) Endometriosis patients produced fewer oocytes (6.6) per cycle when compared to social egg freezing (9.4). Moreover, within the endometriosis patient cohort, those having had surgery produced fewer metaphase II oocytes per cycle and had lower LBRs than those with no surgical intervention prior to the oocyte retrieval.
Age, therefore, should not be the sole significant predictor of vitrified oocyte survival and clinical outcome. Age, patient prognosis and the number of oocytes should be evaluated when predicting oocyte-preservation patient outcomes for a specific population cohort. Cobo proposed that endometriosis patients <35 years would need a total of 20 vitrified oocytes to achieve a 90.8% clinical LBR.(6)
Such studies indicate significant clinical outcome differences amongst patient populations using vitrified oocytes. She thus concluded that the management of patient expectations prior to oocyte preservation and frozen-oocyte replacement cycles should be adapted not only according to patient age, but also to the number of oocytes cryopreserved, patient pathology, and surgical and medical history.
1. Vienna Consensus: report of an expert meeting on the development of ART laboratories performance indicators. Hum Reprod Open 2017; 2: hox011. doi.org/10.1093/hropen/hox011
2. The Alpha Consensus: meeting on cryopreservation key performance indicators and benchmarks: proceedings of an expert meeting. Reprod Biomed Online 2012; 25: 146-167.
3. Forman EJ, Li X, Ferry KM, et al. Oocyte vitrification does not increase the risk of embryonic aneuploidy or diminish the implantation potential of blastocysts created after intracytoplasmic sperm injection: a novel, paired randomized controlled trial using DNA fingerprinting. Fertil Steril 2012: 98: 644-649.
(4) Cobo A, Garrido N, Crespo J, et al. Accumulation of oocytes: a new strategy for managing low-responder patients. Reprod Biomed Online 2012; 24: 424-432.
(5) Cobo A, Garrido N, Pellicer A, Remohí J. Six years' experience in ovum donation using vitrified oocytes: report of cumulative outcomes, impact of storage time, and development of a predictive model for oocyte survival rate. Fertil Steril 2015 ; 104: 1426-1434.
(6) Coello A, Nohales M, Meseguer M, et al. Prediction of embryo survival and live birth rates after cryotransfers of vitrified blastocysts. Reprod Biomed Online 2021; 42: 881-891.