A recent analysis suggests livebirth rates may be 8% lower in fresh embryotransfers with cryopreserved oocytes compared to fresh donor oocytes.

8% reduction on live birth rates in fresh embryo transfers from cryopreserved donor oocytes compared to fresh donor oocytes, suggests a recent analysis by the Society for Assisted Reproductive Technology Clinic Outcome Reporting System, in the US (1).

24663 fresh embryo transfers cycles of donor oocytes were analysed according to whether fresh of cryopreserved oocytes were used for fertilization, with live birth rates in fresh oocytes at 57,5% compared with 49,7% in cryopreserved oocytes. 

Despite the ease of planing, lower cost and easier access in cryopreserved donor oocytes, this significant difference raises several questions about the effectiveness of cryopreserved oocytes in oocyte donation programs. Vitrification and thawing of oocytes has been examined repeatedly in the past and, although safety has been demonstrated, functional and/or morphological changes in the oocytes may account for some of the reported difference. Also, the authors point out the greater use of assisted hatching in cryopreserved oocyte fresh embryo transfers, as there have been some studies in the past suggesting that assisted hatching may be associated with reduced live birth rates.

Another possibility raised in the publication is that the criteria may differ for donors of fresh oocytes compared with donors of cryopreserved oocytes. Oocyte cryopreservation in commercial oocyte banks may follow different criteria, particularly in order to address various phenotypic requests.

The lower live birth rates with cryopreserved donor oocytes, as well as the lower number of surplus embryos compared with fresh donor oocytes raises questions about the effectiveness of cryopreserved donor oocytes in fresh embryotransfers. Despite the fact that these are retrospective data, the sample size is big and reflects real life clinical practice. Consideration should be given to counseling couples undergoing oocyte donation with cryopreserved oocytes and fresh embryotransfer, as livebirth rates may be reduced.

References:

1. Rachel M. Whynott et al. “Fresh embryo transfer after in vitro insemination of fresh vs. cryopreserved anonymous donor oocytes: which has a better live birthrate? A Society for Assisted Reproductive Technology Clinic Outcome Reporting System analysis” (doi.org/10.1016/j.fertnstert.2022.01.008)

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