Conclusion
In conclusion, as a supplementary treatment for fresh embryo transfer, FET is a relatively safe transplantation scheme. Compared with HRT-FET, the NC-FET is more in line with the internal milieu, and the risk of obstetric complications lower. In cases where fresh embryos have failed repeatedly or are not suitable for fresh embryo transfer, NC is recommended for FET to reduce the risk of complications. In this study, there was no significant effect of the three embryo transfer methods on placental structural and pathological abnormalities.