Although fresh embryo transfer (ET) is the norm during assisted reproductive therapies (ART), in the past few years, avoiding a fresh embryo transfer and instead of freezing all the good quality embryos has emerged as an alternative strategy during in vitro fertilization (IVF) cycles (Roque, 2015). The success of IVF depends not only on embryo quality but also on the interaction between the embryo and the endometrium, the implantation. During IVF cycles, there are several concerns about the possible adverse effect of the controlled ovarian stimulation (COS) and the high estradiol (E2) levels on the endometrium, which in turn might have an effect on the pregnancy rates (Shapiro et al., 2011; Roque et al., 2013). It is postulated that during the freeze-all strategy, the cryopreserved embryos are transferred later when the E2 is at physiologic levels and the endometrium presents a physiologic environment. (Roque, 2015). By performing delayed frozen-thawed ET (FET), any adverse effects of COS over the endometrium is thus avoided, and this should lead to better outcomes (Shapiro et al., 2011, Roque et al., 2013; Roque, 2015).
A current perspective of the available literature regarding this subject is that the freeze-all strategy is not designed for all IVF patients. At least two studies show that only patents with polycystic ovary syndrome (PCOS) might be benefited (Chen et al., 2016; Shi et al., 2014). Today, it is reasonable to perform elective cryopreservation of all embryos in cases with a high risk of OHSS development, and inpatient with supra-physiologic hormonal levels during the follicular phase of COS. It is not clear if all the patients that had a normal response and poor responders to COS may benefit from this strategy (Roque et al., 2017).
We questioned this premise at DVIF&G by analyzing our own data from the last three years and we compare the implantation rates between the fresh and the frozen embryo transfers. The implantation rates were favorable and increased during frozen embryo transfers when compared to fresh embryo transfers. The combined data from 2017 and 2018 showed that the frozen implantation rates almost double by comparison to those in a fresh embryo transfer and in 2019 the frozen embryo implantation rates more than double those of fresh, achieving a high 60% rate.
It follows that an increase in implantation rates will lead to a decrease in the average number of embryos transferred. Indeed the average number of embryos transferred in frozen cycles has decreased from 1.5 in years 2017+2018 to an average number of 1.1 embryos in 2019. Whereas, the average numbers of embryos transferred in fresh cycles were higher approximating 2 embryos per transfer than in FET. In light of these results, our patients are advised to proceed with a freeze all cycles in the hope that their goal will be achieved faster and at the same time minimizing the disappointment from a failed embryo transfer.