Fresh vs. Frozen Embryo Transfer: Is Vitrify All a Better Option? A Retrospective Study

Rosli NI, Hing KK, Tham MY, Sim PK, Lim YH, Nadkarni P. Is Vitrify All a Better Option? Poster presented at the ASPIRE (Asia Pacific Initiative on Reproduction) Conference, 2014. KL Fertility Centre, Kuala Lumpur, Malaysia.

Funding and disclosures: No declarations available (conference poster). The authors report no competing interests.

Frozen embryo transfer (FET) has been reported to carry a lower risk of prenatal bleeding, preterm delivery, and low birth weight compared with fresh embryo transfer. Implantation rate may also be improved in a non-stimulated cycle, as controlled ovarian hyperstimulation (COH) can adversely affect embryo-endometrium synchrony. These observations prompted interest in a “freeze-all” strategy: vitrifying all available embryos following egg collection and deferring all transfers to subsequent FET cycles.

The key clinical question this study sought to address was whether, in the same group of patients who experienced both a fresh transfer and a subsequent frozen transfer, the frozen cycle produced meaningfully better outcomes — and if so, whether a policy of vitrifying all embryos might improve cumulative clinical pregnancy rates.

Table 1. Fresh ET vs. Frozen ET outcomes

Using chi-square analysis, clinical pregnancy rate was significantly higher (p < 0.05) and miscarriage rate was significantly lower (p < 0.05) in the frozen embryo transfer group compared with the fresh transfer group.

The significantly higher clinical pregnancy rate and lower miscarriage rate in the FET group are consistent with the hypothesis that COH impairs embryo-endometrium synchrony during a fresh cycle, and that transfer in a subsequent non-stimulated cycle benefits from a more receptive uterine environment.

These findings are broadly consistent with the wider literature. Meta-analyses of randomised controlled trials have found significantly higher live birth and clinical pregnancy rates, and lower miscarriage and OHSS rates, in freeze-all strategies compared with fresh transfer. However, evidence also indicates that the magnitude of benefit is not uniform: the freeze-all advantage is most pronounced in high responders and in women with polycystic ovary syndrome (PCOS), and less clear in women with a typical ovarian response. A 2021 Cochrane review found that for non-PCOS women with a normal ovarian response, freeze-all did not clearly improve live birth rates over fresh transfer, while it did reliably reduce OHSS risk. Current ESHRE guidance reserves elective freeze-all as standard practice specifically for high-risk or high-response groups rather than recommending it universally.

As a 2014 conference poster based on 2012 data, this study predates the more nuanced current view. Its conclusion that there is “a role to vitrify all embryos” reflects the state of evidence at the time and the clear benefit seen in this centre’s early cohort data, but should be contextualised within the subsequent literature as a group-specific rather than universal recommendation.

These data support the use of frozen embryo transfer for patients with vitrified surplus embryos, consistent with current practice. For clinicians weighing a freeze-all strategy at the outset of an IVF cycle, the key patient-level factors to consider are ovarian response profile, PCOS status, and OHSS risk, since these are the populations where current evidence most robustly supports elective freeze-all. For typical responders without these risk factors, fresh transfer remains a clinically supported option.