Embryo transfer consists of inserting the embryos generated in the laboratory into the uterus so that they implant and give way to a pregnancy. With the help of a fine catheter, and under ultrasound control, the medical person will introduce the embryo or embryos into the uterus. It does not require anesthesia and does not cause pain.
Seen in a summarized way, embryo transfer consists of the following steps:
- Clean the vagina with physiological serum.
- Clean the cervix.
- Aspirate cervical mucus.
- Load the embryos into the catheter.
- Introduce the catheter until it reaches the uterus.
- Deposit the embryos in the uterus.
- Withdraw the catheter.
It is important to check and make sure that the embryos have not remained in the catheter.
The number of embryos to be transferred depends on the woman's age and the number of eggs retrieved. Since the implantation rate decreases as the woman ages, more embryos are usually transferred in these cases. Except in cases where donor eggs are used.
Extra or leftover embryos can be frozen and saved for future use, donated to another couple or to research facilities, or discarded.
Embryo transfer can be in the natural cycle or in the substituted cycle. The first difference between the two is the way of carrying out the preparation of the endometrium and the lining inside the uterus. In the natural cycle, the natural estrogens released by the ovaries are used; while in the substituted cycle, it is necessary to administer drugs that cause the formation of these estrogens.