Definition and Overview

Embryo transfer refers to the process of implanting an embryo into a woman’s womb after the reproductive cells have been cultured, become a zygote, and enter the embryonic stage.

The transfer is the last stage of in vitro fertilization (IVF), a reproductive-assisted technology in which the sperm and egg are obtained for fertilization in a petri dish. Once the egg has been fertilized, it then transforms into a zygote, where it undergoes into several rapid divisions of cells. Around three days, it transforms into an embryo. An embryo is called a fetus once it has successfully reached the 8th week of gestation.

Although the process is often described as simple, it’s not that easy since it’s important that the embryos are implanted properly. Otherwise, it may not develop into a fetus, and therefore, no pregnancy can be expected to occur.

The doctor, who is an IVF specialist, should ensure the embryo is placed within the endometrial cavity. This cavity refers to the space inside a lining called endometrium. Both the endometrium and the cavity are found inside the uterus. The cells that make up the lining are renewed every month. If there’s no pregnancy, the lining or membrane is shed off, in which case it becomes a woman’s period (menstruation). However, if the embryo transfer is successful, the lining thickens to ensure it can fully support the development until the baby is carried to full term.

Who Should Undergo and Expected Results

Embryo transfer is performed on women who have successfully passed the rigid criteria for IVF. These women can be a partner who has successfully produced and donated good-quality eggs (although it’s possible that the eggs are donated by somebody else). Sometimes IVF women can reproduce eggs but have a decreased chance of getting pregnant for a number of reproductive issues. The couple may opt to have another person, a surrogate, to carry the baby and thus undergo the embryo transfer.

The procedure is relatively painless. Once the embryo has been implanted into the endometrial cavity, it becomes a wait-and-see period. Around this time, the woman waits until she becomes pregnant. Pregnancy, on the other hand, usually occurs around the 9th day after implantation.

The chances of getting pregnant are affected by many factors, and one of the most important is the age. The younger the woman is, the higher the chances of conceiving, wherein the embryo attaches itself to the wall of the uterus. Based on a 2011 data, a woman who goes through embryo transfer before she hits 35 years old has a 40% chance of getting pregnant—a huge percentage compared to less than 5% if the woman is 45 years old and above.

To further increase the possibility of pregnancy, the specialist may recommend a blastocyst transfer. A blastocyst is an embryo that is around six days old. A blastocyst has more cells and is more stable than a 3-day-old embryo.

How Does the Procedure Work?

The procedure of embryo transfer is likened to that of a pap smear since the specialist needs to access the cervix to reach the uterus and the endometrial cavity. The vagina is kept open with the use of a speculum.

During the procedure, the woman is wide awake and aware. Just like in a pap smear, there’s no need for any medication or anesthesia. However, if it is an ultrasound-guided procedure, it may be necessary to have a half-full bladder for smoother visual.

The embryo for implantation is placed at the tip of a catheter. The catheter then goes into the cervix until it reaches the uterus. Once the tip is already in the correct position, the embryo is carefully ejected. The catheter is then slowly pulled out of the uterus, cervix, and vagina. The specialist then checks the catheter’s tip to ensure there’s no embryo left. Otherwise, the procedure will be repeated.

For a higher chance of pregnancy, multiple embryos may be transferred. However, to avoid excessive multiple pregnancies, experts concur it should be no more than 4 implanted embryos.

During the fertilization, it’s possible to produce several healthy embryos. The client can then choose to either destroy them or keep them for future use. If it’s the latter, the embryos are stored in a very cold environment.

Possible Risks and Complications

The process itself has a very minimal risk that doesn’t affect the success rate of the embryo transfer. These include abdominal cramping after the procedure. The risk, on the other hand, is present after the embryo has been implanted. Of course, the most critical is whether it results in pregnancy. For this reason, researchers are working on a new process of selecting an embryo to be transferred. Called metabolomics, it involves detecting the metabolite levels of a cultured embryo.

References:

  • Lobo RA. Infertility: etiology, diagnostic evaluation, management, prognosis. In: Lentz GM, Lobo RA, Gershenson DM, Katz VL, eds. Comprehensive Gynecology. 6th ed. Philadelphia, Pa: Elsevier Mosby; 2012: chap 41.

  • Goldberg JM. In vitro fertilization update. Cleve Clin J Med. May 2007; 74(5): 329-38.

  • The Practice Committee of the Society for Assisted Reproductive Technology and the Practice Committee of the American Society for Reproductive Medicine. Criteria for number of embryos to transfer: a committee opinion. Fertil Steril. Jan 2013;99 (1):44-46.

  • Jackson RA, Gibson KA, Wu YW, et al. Perinatal Outcomes in Singletons following in vitro fertilization: a meta-analysis. Obstet Gynecol. 2004;103: 551-563.

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