An advanced SWOT analysis of elective vitrification: today's standard IVF procedure

In clinical practice, treatment cycles are routinely started without the intention of undertaking fresh embryo transfer, as the freeze-all strategy is suitable for a multitude of alternative stimulation protocols as well as preimplantation genetic testing of embryos. Based on strengths, weaknesses, opportunities and threats (SWOT) analysis, it was evaluated whether a freeze-all strategy may be advised for all patients regardless of their (predicted) ovarian response. Therefore, the latest literature including the outcome of all randomized controlled trials (RCT) and their combined analysis were reviewed. Only two large trials, both from China, were considered conclusive and showed (following first embryo transfer) a higher chance of live birth following elective vitrification in comparison with fresh embryo transfer in women with polycystic ovary syndrome and in ovulatory women with a good prognosis. The other six trials showed either no difference in clinical outcome or were inconclusive by design. It is concluded that elective vitrification is likely favourable for high responders as it results in an improved chance of live birth following single embryo transfer, and is likely equally successful for normal responders. One trial in low responders indicated that the live birth rate may be compromised, which needs further confirmation in the future. This SWOT analysis of embryo transfer deferral also concluded that this approach allows the number of oocytes per stimulation cycle to be maximized safely in order to improve the chance of pregnancy. To minimize the risk for obstetric and perinatal complications in frozen-thawed embryo transfer cycles, (modified) natural cycles should be considered as the preferred approach for regular cycling women.