Transferring the embryos in the same cycle in which the ovaries have been stimulated can lead to the destructuring of the endometrium, since it would be stimulated by several follicles and this could lead to a loss of receptivity.
For this reason, more and more embryo transfers are being done on a deferred basis, that is, in a cycle following ovarian stimulation. In this case, the embryos are frozen while waiting for a new cycle in which the endometrium is optimal for implantation.
The transfer of cryopreserved embryos can be done in a natural cycle or in a substituted cycle, with the contribution of exogenous hormones.
In the case of the natural cycle, the natural growth of the endometrium is used throughout the menstrual cycle, which avoids the side effects of medication, reduces the level of stress on the patient and also has a lower economic cost.