Embryo Transfer: Procedure and Types

Embryo transfer is defined as a step in the process of assisted reproduction in which embryos are planted into the uterus of a female with the intent to establish a pregnancy. In another word, it is the method performed to place the embryo in the uterus where its development will take place. This technique is often used in connection with In vitro fertilization (IVF). It may be used in humans or animals, in which situations the goals may vary. Embryo transfer can be done on day 2 or day 3, or later in the blastocyst stage. It was first performed in 1984. Factors that can affect the success of embryo transfer consist of endometrial receptivity, embryo quality, and embryo transfer technique. In this article, we will learn about the procedure and types of Embryo Transfer.

Also check out- Gel Electrophoresis- A Separation Technique – My Biology Dictionary

HISTORY:

The very first transfer of an embryo from one human to another which resulted in pregnancy was reported in July 1983. On 3 February 1984, it subsequently led to the announcement of the first human birth. The embryo transfer procedure was performed at the Harbor UCLA Medical Center. Under the direction of Dr. John Buster and the University of California at Los Angeles School of Medicine.

This scientific discovery established standards and became an agent of change for women with infertility. And also for the women who did not want to pass on genetic disorders to their children. Donor embryo transfer has given women a mechanism to become pregnant and give birth to a newborn that will contain their husband’s genetic makeup.

Previously to this, thousands of women who were infertile had adoption as the only path to parenthood. This set the stage to allow open and candid conversation about embryo donation and transfer. This discovery has given way to the donation of human embryos as a common practice similar to other donations such as blood and major organ donations. At the time of this announcement, the event was captured by the majority of news carriers and fueled healthy debate and discussion. This practice impacted the future of reproductive medicine by forming a platform for further advancements in woman’s health.

Embryo transfer established the technical foundation and legal-ethical framework surrounding the clinical use of human oocyte and embryo donation. The mainstream clinical practice has evolved over the past 25 years.

PROCEDURE:

The procedure of embryo transfer is very simple. The method starts by placing a speculum in the vagina to visualize the cervix, which is cleansed with saline solution or culture media. A transfer catheter is loaded with the embryos and handed to the clinician after confirmation of the patient’s identification. Through the cervical canal and advanced into the uterine cavity, the catheter is inserted. Several types of catheters are used for embryo transfer. Anyhow, there is good evidence that using a soft counter to a hard transfer catheter can increase the chances of clinical pregnancy.

Steps:

There is good and consistent evidence of use in ultrasound guidance. It makes an abdominal ultrasound to ensure correct placement which is 1–2 cm from the uterine fundus. There is evidence of an important increase in clinical pregnancy using ultrasound guidance compared with only “clinical touch”. As well as performing the transfer with hyaluronic acid enhances the transfer media. Generally, anaesthesia is not required. Single embryo transfers in distinct require accuracy and precision in placement within the uterine cavity. The best target for embryo placement is known as the maximal implantation potential point. It is identified using 3D/4D ultrasound. Anyhow, there is limited evidence that supports the deposition of embryos in the midpart of the uterus.

After insertion of the catheter, the contents are released and the embryos are deposited. Limited evidence supports making test transfers before performing the procedure with embryos. After removal, the duration that the catheter remains inside the uterus does not affect pregnancy rates. Limited evidence suggests avoiding negative pressure from the catheter after removal. After withdrawal, the catheter is handed to the embryologist, who observed it for maintained embryos.

A must read- Microparticle Bombardment – BIOLISTICS (Gene Gun) (mybiologydictionary.com)

In the process of zygote intrafallopian transfer (ZIFT), eggs are detached from the woman, fertilized, and then placed in the woman’s fallopian tubes in place of the uterus.

TYPES:

The same process is followed every time to extract and fertilize the eggs during IVF. Once fertilization has occurred, there are many options for embryo transfer:

• Fresh embryo transfer:
  

After fertilization, eggs are cultured for 3-5 days. The perfect embryos are chosen for direct transfer to the woman’s uterus.

• Frozen embryo transfer: 

Any healthy embryos that were not used in the first transfer can be frozen and stored or saved for future use. These can be melted and transferred into the uterus. In some cases, the first embryo transfer can also be a frozen embryo transfer if all embryos formed are frozen.

• Cleavage (Day 3) Stage Embryo Transfer: 

These are called such because the cells in the embryo are dividing (or cleaving). But the embryo itself is not growing in size. This stage is usually reached around day 3, but it may happen on day 2 or 4. They have generally referred to simply as “day three embryos.”

• Blastocyst (Day 5) Stage Embryo Transfer:

It is an embryo that has developed into a single-layered sphere of cells by encircling a fluid-filled cavity with a heavy mass of cells grouped together.  Blastocysts contain anywhere from 60 -120 cells. This mostly occurs on day five, but may also happen on day 6, 7, or even 8. By this stage, the embryo has differentiated into two types of cell:  the trophectoderm (the cells on the periphery or edge of the embryo that forms the placenta) and the inner cell mass (ICM) (the heavy mass of cells on the inside that forms the fetus if the embryo implants).

• Single Embryo Transfer (SET or eSET):

 A(n) (Elective) Single Embryo Transfer is the process of transferring only one embryo into a woman’s uterus. It offers a decreased chance of multiples while maintaining a very similar rate of pregnancy. Due to the decrease in risk of an eSET along with having a very similar rate of pregnancy, it quickly becomes the gold standard practice for transferring embryos with an IVF procedure.

Image source: babygest.com

• Multiple Embryo Transfer: 

A transfer of multiple embryos is actually very simple to transfer of more than one embryo. At the same time, this can be done for some, there are very strict guidelines that restrict the transfer of multiple embryos. Transferring a large number of embryos (or even more than one in some instances) can get a clinic shut down in today’s day and age.

To conclude, Embryo transfer is the method performed to place the embryo in the uterus where its development will take place. Embryo transfer provides at least these basic goals: to backing a genetic line which has difficulty reproducing, to develop disease free unborn or to manipulate genetically. The procedure of embryo transfer can vary as per the condition.

Keep reading for more!

Team MBD

Read more- Marine Biotechnology: An emerging field – My Biology Dictionary

Reference: Embryo Transfer – an overview | ScienceDirect Topics