Outcomes of embryo vitrification at different developmental stages: Evaluation of 2412 warming cycles

In vitro Fertilization Outcomes of Frozen-thawed Embryo Transfer with Hatched Blastocysts versus with Hatching Blastocysts

This study aimed to elucidate the effect of hatching status on in vitro fertilization (IVF) outcomes in frozen-thawed blastocyst transfer cycles. Frozen-thawed embryo transfer (FET) cycles performed at a single fertility center between 2016 and 2021 were retrospectively assessed. Analyses were restricted to 6,821 frozen-thawed blastocyst transfers in women aged 24-47 years. For optimal comparability, double embryo transfer (ET) cycles consisting of one hatching and one hatched blastocyst were excluded. The implantation and pregnancy rates were evaluated and compared between the hatching and hatched blastocyst transfer groups based on patients' age (<38 vs. ≥38 years), blastocyst grade (good vs. bad grade), and the number of transferred embryos (single ET vs. double ET). Hatched blastocyst transfer was associated with higher implantation and clinical pregnancy rates in the single ET group (15.7% and 15.6%, respectively; p<0.001). The transfer of two hatched blastocysts had higher implantation and clinical pregnancy rates compared to the transfer of two hatching blastocysts (19.5% and 20.4%, respectively; p<0.001) in the double ET group. In the hatched blastocyst transfer group, the clinical pregnancy and implantation rates were higher, regardless of each woman's age and embryo quality. The IVF treatment outcomes were improved when the blastocysts were hatched during FET cycles. Hence, hatched blastocyst transfer in FET cycles could be considered a superior method in IVF practice.

Determinants of Embryo Implantation: Roles of the Endometrium and Embryo in Implantation Success

Both uterine endometrium and embryo contribute to implantation success. However, their relative role in the implantation success is still a matter for debate, as are the roles of endometrial receptivity analysis (ERA), endometrial scratch (ES), endometrial microbiome, and intrauterine or intravenous measures that are currently advocated to improve the implantation success. There is insufficient evidence to suggest that the endometrium is more important than the embryo in determining the implantation success and the utility of these measures, especially when euploid embryos are transferred is limited. Although embryo implantation on epithelium other than the endometrium is a very rare event, evidence suggests that embryo implantation and growth is not limited to the endometrium alone. Embryos can implant and develop to result in livebirths on epithelium that lacks the typical endometrial development present at implantation. Currently, the role of embryo euploidy in implantation success is underappreciated. At a minimum, it is the author's opinion that until robust, definitive studies are conducted that demonstrate benefit, reproductive endocrinologists and infertility specialist should be prudent in the way they counsel patients about the utility of ERA, ES, and other measures in improving implantation success.

When to Transfer Embryos if There Is Only 1 or 2?

The latest reports suggest that it is better to transfer embryos to the uterus on day five of preimplantation development compared to other days of development, but it is not clear if this stands when there are only one-two embryos obtained in the cycle. Therefore, to address this issue, we performed a retrospective study of such cycles. Our study included all of the stimulated IVF/ICSI cycles performed at our institution in the period between 1 January 2004 and 31 December 2018 in which one-two embryos were obtained in the IVF/ICSI cycle and met our inclusion criteria, and we compared the data between day three and day five embryo transfer (ET). The analysis revealed that the day three ET group of patients was significantly older (p < 0.001), were administered a significantly higher dose of gonadotrophins (p = 0.015), and retrieved a lower mean number of aspirated oocytes per cycle (p < 0.001) and lower mean number of embryos (p < 0.001). The birth rate per ET was significantly higher in the day five ET group (p = 0.045) and further analysis indicated that this could be due the trend observed in a group of patients under 36 years old, while in older patients there was no such difference. To conclude, our retrospective study indicates that it might be better to perform ET on day five instead of day three when there are only one-two embryos obtained in the cycle, but probably only when patients are under 36 years old.