However, some people are told that they are not suitable for fresh embryo transfer after egg retrieval and embryo acquisition, and that they need to freeze the embryos first and wait patiently for some time. What are the reasons why a doctor would recommend cancelling a fresh embryo transfer? Fresh embryo transfer is not recommended for patients at risk of ovarian hyperstimulation syndrome (OHSS), which is a common complication of ovarian hyperstimulation after ovulation promotion, mostly seen in patients with high number of eggs and high estrogen levels after ovulation promotion. Pregnancy can aggravate ovarian hyperstimulation syndrome, thus putting the mother in a more dangerous situation. However, this is a self-limiting disease and with prolonged time after egg retrieval, the symptoms will gradually improve with the treatment of the doctor, and the risk associated with it is usually greatly reduced after the onset of menstruation. Therefore, in patients with a risk of OHSS, doctors often do not recommend transfer, and it is safe for both the mother and the fetus to first treat the OHSS and then transfer the frozen embryos after the maternal state has stabilized. Therefore, it is worth waiting for safety. Fresh embryo transfer is not recommended for problems with the endometrium. Once the embryo is obtained, it is equivalent to obtaining the “seed”, and the soil in which the seed is planted —– needs to be evaluated to see if the “endometrium” is qualified. Endometrial polyps, poorly formed endometrium, endometritis, complete longitudinal uterine septum, etc. indicate that there may be problems with the “soil” and that it is not suitable for planting the “seed” for the time being. In such cases, doctors often recommend that the patient first treat the endometrium before embryo transfer. Therefore, in order to increase the success rate, it is important to clean up the “soil” first and then plant the seeds. The endometrium is not synchronized with the embryo development and progesterone is elevated before egg retrieval. Progesterone levels generally rise after ovulation, and progesterone acts on the endometrium to transform it into a “fertile” state, thus creating a “window of opportunity” for embryo implantation. This transformation needs to take place after ovulation, which is “consistent” with the period of embryo formation, and either too early or too late in the “window” of implantation will affect the implantation of the embryo. The timing of the “window” of implantation is influenced by progesterone. In some cases, the progesterone may be elevated before ovulation, resulting in the early transformation of the endometrium, which may cause the “window” of implantation to be out of sync with the embryo development, thus reducing the success rate. In addition, in addition to elevated progesterone, slow embryo development is also a factor, such as a 4-cell embryo on day D3, and embryo freezing may be recommended. Other factors: hydrocele in the fallopian tube, huge fibroids in the uterus, and other medical conditions that make the body unsuitable for conception. Fluid in the fallopian tube has adverse effects on embryo implantation, as we have explained in detail in the previous section. In this case, embryos need to be frozen and the fluid will be treated before embryo transfer. In addition, the fibroids need to be treated first if they are huge, if they affect the morphology of the uterine cavity, or if they may increase further after conception. If other diseases are found in the body, such as high fever with flu (which cannot be recovered in the short term) or other organ system diseases that need to be treated first, it is also recommended to freeze the embryos and transfer them after the body recovers.