Embryo Transfer (ET)
Embryo Transfer (ET)
What Is Embryo Transfer?
Embryo transfer is the final and most decisive stage of in vitro fertilisation (IVF), during which one or more embryos are placed into the woman’s uterus, marking the
beginning of a possible pregnancy. The procedure is usually performed 2–5 days after fertilisation of the eggs in the laboratory, when the embryos have reached the
corresponding stage of development. On day 5 or 6, embryos are at the blastocyst stage. It is worth noting that embryo transfer may involve both “fresh” embryos as well as
cryopreserved (frozen) embryos, depending on the protocol followed and the clinical scenario.
When Is It Performed?
Embryo transfer is most commonly carried out on day 2, 3, 5, or 6 after fertilisation in the laboratory. The choice of the transfer day depends on embryo quality and development, as well as the protocol used in each case. On day 3, embryos typically reach the 6–8 cell stage and can be transferred, while on day 5 or 6, they have developed into blastocysts, offering increased chances of implantation. Day 4 is rarely used for transfer because embryos are in the morula stage, a transitional form between the cleavage and blastocyst stages that is difficult to evaluate morphologically. Please note that frozen blastocyst transfer is scheduled in a cycle where appropriate endometrial preparation has been performed, in order to improve implantation chances.
How Is Embryo Transfer Performed?
On the day of embryo transfer, the woman attends with a full bladder, to facilitate ultrasound guidance during the procedure. In a gynaecological examination position, a thin, relatively firm catheter is introduced through the cervix up to the entrance of the uterine cavity. The embryos are then transferred—and gently placed inside the uterus—using a second, flexible catheter that passes through the cavity via the first catheter. The procedure takes only a few minutes and does not require anaesthesia. Afterwards, the woman rests for a short time and continues luteal-phase support with progesterone, oestradiol and other supplements to enhance the chance of implantation. Proper uterine preparation and precision in embryo transfer technique play a crucial role in IVF success.
The decision regarding the number of embryos to transfer is made based on the woman’s age, embryo quality and her medical history, with the goal of achieving pregnancy with the lowest possible risk of multiple gestation.
Symptoms by Day (Detailed)
After embryo transfer,the embryo(s) will implant into the endometrium by the latest by the following day and, at the same time, levels of certain hormones will increase to support pregnancy. Mildsymptomsmay occur during the implantation process. Specifically:
● Day 1: The blastocyst begins to “hatch” from its outer оболка (zona pellucida)—a process called hatching—and its cells continue to divide and grow.
● Day 2: Hatching continues and the blastocyst starts to “attach” to the endometrium.
● Day 3: The blastocyst begins to “invade” the endometrium and implantation starts. At this stage, light bleeding may occur, which can be normal.
● Day 4: The blastocyst moves deeper into the uterus and begins to receive nourishment from the endometrial blood supply. Bleeding on the 4th day after embryo transfer may be heavier; however, the absence of bleeding does not mean implantation has failed.
● Day 5: Implantation is considered complete and embryo development continues. Cells begin to differentiate into those that will form the placenta and those that will form the embryo.
● Day 6: The placenta begins producing beta human chorionic gonadotropin (β-hCG), which stimulates progesterone production by the ovaries to support the developing embryo.
● Day 7: The embryo continues to grow and the placenta secretes more β-hCG.
● Day 8: Development progresses rapidly and β-hCG levels continue to rise.
● Day 9: β-hCG levels are high enough to be detected in a blood pregnancy test.
Many women experience mild cramps and bleeding after embryo transfer. Symptoms similar to premenstrual syndrome may also occur, such as breast tenderness, nausea, and fatigue. These may indicate either early pregnancy or side effects from fertility medications.
β-hCG levels after embryo transfer are the most reliable indicator of successful implantation and one of the earliest signs of pregnancy. β-hCG is produced by the placenta and can be detected via a blood test approximately 9–10 days after a blastocyst transfer, or slightly later in the case of day-3 embryos. Low values or a slower-than-expected rise may suggest failed implantation or a complication; therefore, hCG results must always be assessed by a specialised gynaecologist in the context of the patient’s history and overall treatment plan.
What Preparation Is Required?
Preparation before embryo transfer typically includes hormonal therapy with oestrogens and progesterone to support optimal endometrial development for implantation, as well as regular monitoring with ultrasounds and blood tests. In addition, a balanced diet, gentle exercise, and stress management are recommended to improve overall physical and mental wellbeing. On the day of embryo transfer, a full bladder helps ensure accurate ultrasound guidance. All of these factors contribute to implantation success.
What Should We Be Careful About Afterwards?
Every woman is different, and needs after frozen blastocyst embryo transfer vary by case. In the past, continuous bed rest until the pregnancy test was considered necessary; however, we now know that prolonged rest has no proven benefit for the outcome. Instead, a balanced approach that combines gentle rest with a gradual return to daily activities is considered more beneficial. Therefore, the following are generally recommended:
● Rest for about 20 minutes after embryo transfer and, for the next 2–3 days, continue your routine at a more relaxed pace.
● Avoid intense exercise and replace it with gentle walking.
● Avoid smoking and alcohol consumption.
● Return to work, unless there are different instructions from your obstetrician-gynaecologist.
The obstetrician–surgeon gynaecologist D. Koleskas, M.R.C.O.G., C.C.T., has excellent theoretical training and more than 20 years of clinical experience in obstetrics and gynaecology. He specialises in human reproduction and provides infertility treatments at the assisted reproduction centre “Biogenetic Centre”. To learn more about embryo transfer, please contact the doctor and schedule your appointment.
