In the Vitro fertilization process, embryo transfer is the final step. It's an extremely crucial procedure. No matter how perfect the IVF laboratory culture environment is, a poorly executed embryo transfer might spoil everything. The precise implantation of embryos near the center of the endometrial cavity — with minimal stress and intervention – is critical throughout the entire IVF cycle.
The embryo transfer procedure seems very similar to a Pap smear for the woman. There should be no pain and no sedation or other drugs are required. We use a moderately full bladder for embryo transfer. This helps in 2 important ways. It allows good ultrasound visualization of the catheter which helps with smooth and proper transfer of the embryos to the best location, and it also unfolds the (anteverted, “tipped up”) uterus to a more accommodating angle,making the process smoother and less traumatic for the uterine lining and the embryos. The embryo transfer catheter is loaded (see video of this) with the embryos and the physician passes it through the cervical opening up to the middle of the uterine cavity. Abdominal ultrasound is used simultaneously to watch the catheter tip advance to the proper location. It is sometimes difficult to keep the tip of the catheter in the exact plane of the ultrasound beam at all times – but it is very important to control the proper placement of the embryos (see the video above).
When the catheter tip reaches the ideal location, the embryos are then “transferred” (squirted out of the catheter) to the lining of the uterine cavity (endometrial lining) by the infertility specialist physician. After the embryos are transferred, the catheter is slowly withdrawn and checked under a microscope for any retained embryos. If an embryo is retained in the catheter (uncommon) the transfer procedure is repeated immediately and the catheter is checked again.
Proper location for placement of the embryos at transfer
Research has been done to determine the optimal location to place the embryos in the uterine cavity. Basically, the middle of the endometrial cavity – half way from the internal os of the cervix to the uterine fundus (top of cavity) – is the best place. Care should be taken to keep the catheter between the top and bottom layers of the endometrium and not to allow it to dissect under the endometrial surface. This is called subendometrial embryo transfer. Pregnancies will occur with subendometrial placement of the embryos, but success rates are lower.
Smooth, efficient and effective embryo transfer Best with a moderately full bladder for good ultrasound visualization and a better angle During the embryo transfer procedure the Wallace catheter is seen in the cervix and uterine lining (below the yellow lines). The embryos are released from the catheter tip – at “L”. Minimal angle between the cervix and uterus (green line).
The Embryo transfer process appears to be very similar to a woman's Pap smear. For embryo transfer, experts recommend a fairly full bladder. This is beneficial in two ways. It allows for better ultrasound visualization of the catheter, which aids in the smooth and proper transfer of the embryos to the best possible location, as well as unfolding the uterus to a more inclusive angle, making the process as smooth as possible and less distressing for the uterine wall and embryos.
The ivf embryo transfer catheter is stocked with embryos and passed through the cervical incision to the center of the uterine cavity by the physician. Simultaneously, abdominal ultrasonography is used to monitor the catheter tip's progress to the right position. It can be difficult to keep the catheter tip in the exact line of the ultrasound waves at all times, but it is critical to ensure that the embryos are properly placed. The embryos are “forwarded” to the lining of the uterine cavity by the infertility specialist physician after the catheter point reaches the proper spot.
After the embryos have been transferred, the catheter is carefully removed and any remaining embryos are examined under a microscope. If an embryo remains in the catheter (which is unusual), the embryo transfer operation is immediately resumed and the catheter is examined once more.
A healthy human embryo will hatch from its shell on day 5-7 after fertilization and implant within hours after hatching out. So actual invasion of the embryo with attachment to the uterine wall occurs about 2-5 days after a day 3 transfer and within 1-3 days after a day 5 transfer.
At our IVF clinic, the number of embryos to be transferred is decided by the couple after a discussion with the physician regarding their embryo quality and how it impacts on the risks for multiple pregnancy versus the risk of failing to conceive at all. As female age increases, the implantation rate of the embryos tends to decline. This means that the chance that an embryo will implant drops gradually (and progressively) as the female partner ages beyond about 32 years old.
On the baby side of things, a singleton pregnancy is safest. So, in general, we would prefer that only one fetus actually implants and continues development. However, because couples fear failing IVF more than they fear the risks of twins, the majority decide to replace back 2 embryos when the female partner is under 38, 2 or 3 embryos when she is 38-40, and 3 or 4 (if they have that many) if she is 41 years old or more. Transferring this number of embryos seems to result in a “reasonable” balance of high overall pregnancy success rates, and low rates of high-order multiple (triplets or more).
The number of embryos to be transferred is selected by the couple following a discussion with the physician about the quality of their embryos and how it affects the chances of multiple pregnancies vs the danger of not conceiving at all. During the Embryo transfer process, the implantation rate of embryos tends to decrease as a woman's age increases. This means that once the female spouse reaches the age of 32, the chances of an embryo implanting decline slowly.