When an in vitro fertilization (IVF) cycle is performed, the last step is embryo transfer. By means of this procedure, the embryo is introduced into the patient's uterus, with the objective of implanting and obtaining gestation.
For this process to be successful, the uterine endometrium must be prepared and receptive and, for this, there are two options: to perform the transfer in a natural or substituted cycle.
When a substituted cycle transfer is performed, the patient is administered estrogens and progesterone for endometrial preparation. On the other hand, if a natural cycle transfer is performed, the estrogens and progesterone produced by the patient's ovaries will prepare the endometrium for implantation.