The final and pivotal phase of in vitro fertilization (IVF) is the transfer of an embryo into the prepared uterine lining for implantation – a procedure known as embryo transfer (ET).
What is embryo transfer, and why does it matter?
Conception naturally unfolds within the female reproductive system: an egg meets sperm, leading to embryo implantation in the uterine lining (endometrium), sparking the onset of pregnancy.
The IVF journey encompasses lab-based fertilization (in vitro), embryo nurturing, and transfer at the blastocyst stage into the uterine cavity.
Essentially, embryo transfer aims to identify the most promising embryo from those fertilized in vitro and transfer it into the primed uterus for implantation.
Even minor missteps during this process can nullify prior efforts, emphasizing the critical nature of this stage.
There are two primary approaches:
- “Fresh” embryo transfer involves implanting an embryo without freezing, ideal when the uterine lining is receptive.
- Thawed embryo transfer (the cryo-protocol): embryos are cultured to blastocyst stage, frozen, then transferred.
Indications for IVF with Cryo-Protocol are:
- When obtaining not one, but multiple embryos. This allows for the use of embryos in a “deferred motherhood” program.
- In the presence of a disease in one of the spouses (for example, an oncological disease).
- For conducting preimplantation genetic testing (PGT) of embryos.
- In the presence of adverse factors (unpreparedness of the uterine epithelium for implantation, in cases of ovarian hyperstimulation syndrome, etc.)
Embryo Transfer Stages
Embryo transfer involves following a specific sequence of actions:
- Cultivation of embryos to the blastocyst stage, selection for transplantation.
- Pharmacological preparation of the female body for pregnancy by creating favorable conditions for implantation (measuring endometrial thickness and assessing its condition; improving their parameters).
- Directly the embryo transfer procedure.
- Observation and support stage during the early pregnancy period.
Embryo Selection
For a long time, the assessment of embryos for transfer was based on morphological indicators. Embryologists determined embryos based on scores reflecting their maturity, division characteristics, cell quality, and content. Embryos with high scores were prepared for embryo transfer. Since cryo protocols were imperfect, several embryos were transplanted. As a result, undesired and medically burdensome multiple pregnancies developed, necessitating embryo reduction.
Today, embryo selection for transfer is performed using preimplantation genetic testing for aneuploidy (PGT-A). The method involves determining the embryo’s chromosomal status at the blastocyst stage using Next Generation Sequencing (NGS) technology.
The methodology is as follows:
- Embryos are cultured for 5-6 days until the blastocyst stage (approximately 100-150 cells).
- Trophoectoderm (the future placenta) cell biopsy is performed (the future placenta).
- Direct genetic testing of the embryo’s trophoectoderm cells for chromosomal anomalies (PGT-A) and monogenic diseases (PGT-M) using Next Generation Sequencing (NGS) technology.
- Embryos with normal chromosomal status (after PGT-A) or screened for inherited disorders (after PGT-M) are prepared for transfer.
PGT technology has nearly a 100% accuracy rate and enhances IVF efficiency. PGT-M prevents the birth of a child with inherited diseases (such as cystic fibrosis, hemophilia, spinal muscular atrophy, etc.) Technologically, PGT also provides information about the embryo’s gender. Since PGT requires several days to obtain results, the tested embryos are preserved using cryopreservation.
Procedure Protocol
The embryo transfer procedure follows this sequence:
- On the appointed day, the woman arrives at the clinic for the procedure.
- The patient is positioned in a chair, and the room is equipped with an ultrasound (US) machine.
- The selected embryo is placed in a specialized thin catheter (a thin, flexible plastic tube) with a nutrient medium.
- The cervix is exposed using mirrors, while simultaneously applying the US sensor to the abdomen to monitor the embryo transfer procedure.
- The catheter is inserted into the vagina, through the cervical canal, into its cavity.
- Under US guidance, the tip of the catheter is maneuvered to the chosen area of the endometrium as determined by the reproductive specialist, where the embryo is then injected.
- The catheter is gently removed.
- Following the embryo transfer, the patient is advised to remain in bed for an hour, followed by a semi-recumbent position for the next two to three days.
The procedure typically lasts up to 15 minutes. Anesthesia is not required; however, the doctor may offer a sedative to reduce the patient’s stress and anxiety.
Here are some recommendations for women undergoing embryo transfer.
Implantation of embryos typically occurs two to three days after transfer. A pregnancy test should be taken 10-14 days post-embryo transfer.
Factors Affecting the Success of Embryo Transfer
The success of the procedure depends on several factors:
- Embryo selection. Morphological assessment and preimplantation genetic testing (PGT-A) allow for the selection of the most viable and fully developed embryo, maximizing its chances of successful implantation.
- Preparation of the uterine endometrium. Creating a hormonal environment conducive to embryo implantation and subsequent pregnancy support.
- Subsequent pharmacological pregnancy support.
Thanks to the expertise of doctors and embryologists, over 90% of couples at ICSI Clinic become happy parents.
Why Embryo Implantation Fails: How to React to Absence of Pregnancy
Reasons for failed implantation and pregnancy:
- Patient’s age (over 40 years old);
- Obesity;
- Chronic illnesses complicating the course of the IVF program;
- Harmful habits in one or both spouses.
In case of IVF program failure, doctors will carefully analyze all possible factors and take them into account when planning the next program.
Conclusions
Embryo transfer, the procedure of placing an embryo into a woman’s uterine cavity, marks the final and critical stage of the IVF program. Thoroughly following all procedure requirements increases confidence in achieving a positive pregnancy test.
The success of embryo transfer relies on embryo selection and preparing the uterine lining for implantation.
Utilizing preimplantation genetic testing (PGT-A) allows for the selection of genetically healthy embryos at the blastocyst stage. Consequently, there is no need to transfer all embryos, reducing the risk of medically challenging multiple pregnancies.
To enhance the efficiency of embryo transfer, our doctors employ protocols to optimize the uterine lining for implantation, creating an optimal ‘window of receptivity’ for increased implantation success.
The embryo transfer procedure is performed on an outpatient basis and typically lasts up to 15 minutes. Under ultrasound guidance, the reproductive specialist guides the catheter with the selected embryo to the chosen area of the endometrium, gently releasing it into the uterine lining.
Pregnancy confirmation is conducted through chorionic gonadotropin level testing on the 10th to 14th day post-implantation. In case of a negative result, planning for the IVF program should consider the identified cause.
Sources:
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- Simon A, Laufer N. Assessment and treatment of repeated implantation failure (RIF). J Assist Reprod Genet. 2012 Nov;29(11):1227-39. doi: 10.1007/s10815-012-9861-4. Epub 2012 Sep 14. PMID: 22976427; PMCID: PMC3510376.
- D’Angelo A, Panayotidis C, Alteri A, Mcheik S, Veleva Z. Evidence and consensus on technical aspects of embryo transfer. Hum Reprod Open. 2022 Sep 6;2022(4):hoac038. doi: 10.1093/hropen/hoac038. PMID: 36196080; PMCID: PMC9522404.
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- Saravelos SH, Li TC. Embryo transfer techniques. BestPract Res Clin Obstet Gynaecol. 2019 Aug;59:77-88. doi: 10.1016/j.bpobgyn.2019.01.004. Epub 2019 Jan 11. PMID: 30711373.
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