Single embryo transfer is a procedure that works to achieve a healthy pregnancy. In vitro fertilization, whereby egg cells are fertilized by sperm cells outside of the body, has become an indispensable part of infertility management, especially after conventional medications and procedures have already failed. Single embryo transfer is a step in the more general procedure of in vitro fertilization. With the intent to establish pregnancy, an embryo fertilized through in vitro fertilization is transferred from a test tube to the uterus, where it is hoped that the embryo will successfully develop into a mature fetus.
If you are considering undergoing single embryo transfer, it is best that you know the general procedure involved in it. The procedure begins by directly visualizing the cervix using a speculum inserted by an obstetrician-gynecologist to your vagina. A soft catheter filled with embryos destined for transfer is then passed through your cervix to enter your uterus. The obstetrician-gynecologist will concurrently use an abdominal ultrasound to confirm that the catheter is correctly and precisely placed inside the cavity of the uterus, then expel the catheter’s load of embryos into the uterus. Immediately upon withdrawal of the catheter, an embryologist will inspect the catheter to determine if there had been any retained embryos.
Embryos are usually transferred three days after fertilization, during the eight-cell stage. In some cases, embryo transfer can be delayed an additional two to three days so that the blastocyst stage will be the one introduced to the uterus.
Fresh and Frozen Embryos
An embryo is considered fresh when it is transferred during the same menstrual cycle as the harvested egg. It is essential that the uterine lining is adequately prepared prior to embryo transfer in order to increase the chances of a successful implantation. Therefore, when using fresh embryos, transfer is usually done during the luteal or secretory phase of the menstrual cycle, when the uterine lining is under the influence of the luteinizing hormone.
On the other hand, a frozen embryo has been fertilized in a preceding menstrual cycle and eventually frozen or cryopreserved. Frozen embryos are then carefully thawed just prior to transfer. Unlike in fresh embryo transfer, your uterine lining is more unpredictable if you will undergo frozen embryo transfer. Hence, you would first be given hormonal therapy to “prime” your uterine lining and make it more conducive for implantation. Usually, estrogen is given for two weeks, and this is followed by progesterone therapy.
In studies conducted by several teams of scientists, it was suggested that frozen embryo transfer might actually be safer and more beneficial than fresh embryo transfer. This goes against the common notion that fresh is better than frozen. Based on studies, babies from fresh embryo transfers have a high probability to be born prematurely and to be of a lower birth weight. In addition, other studies have uncovered that fresh embryo transfers may have higher rates of stillbirth and early death.