A number of patients aren’t too sure about the medical details involved in their IVF cycle. At times, this also means they end up using medical terms incorrectly. Most patients tend to use the terms embryo transfer and embryo implantation interchangeably and aren’t sure whether there is any difference between the two.
Embryo transfer is a very simple clinical procedure in which the IVF doctor transfers your embryo/s into your uterus with the use of an embryo transfer catheter. This is essentially a mechanical step; it involves transferring the embryo from the Petri dish, into your uterus. Implantation , on the other hand, is a complex biological process that takes place in the uterus.
When the doctor transfers the embryos on Day 3, they have around 8 cells; If all goes well, these cells will continue to divide in utero, until the time they form blastocysts. Once these hatch, the embryo cells then embed themselves in the uterus’ walls. Typically, this occurs on Day 6 or Day 7 post egg collection. Implantation is a silent biological in utero process and we have no control over it; it has 3 phases:
• Apposition, when the embryo moves towards the endometrium
• Adhesion , when the blastocyst sticks to the endometrium
• Invasion, when the blastocyst buries into the endometrium
All these phases are dependent on a perfectly synchronized exchange of molecular signals that takes place between the embryo and the endometrium – what is called molecular cross-talk. Each one of these stages is crucial and they have to take place in a sequential manner. There is no magic “Cinderalla hour” at which time implantation occurs – it’s a continual process. Also, patients need to remember that we aren’t able to either track or monitor implantation , and there is no way we can influence it either .
Unpredictable Embryo Behavior
Of course, as part of the procedure , we give you progesterone and estrogen to prepare the lining of your uterus for the implantation. However, when it comes to the matter of whether your embryos will implant or not and how many of them will implant, it’s something we can neither predict nor control. If you stop to think about it, this isn’t surprising at all. The embryo is a microscopic ball of cells and there is no way we are able to track what these cells do once they have been transferred into the uterus.
The Genetic Abnormality Factor
So, why then does it happen that all the transferred embryos don’t implant? This may sound like a very “un-medical” explanation, but the fact is that human reproduction can be quite inefficient. Isn’t it true that not all fertile couples get pregnant every time they have sex in their fertile period?
In most instances, a genetic abnormality is the cause of failed implantation. This is actually a natural defense mechanism of our bodies to prevent the birth of an abnormal baby. Of course, these defects don’t really follow any set pattern and are quite random, but they are more common in older women. This occurs because the eggs of older women tend to have a greater number of genetic abnormalities, as they have aged . We still cannot screen for most of these genetic defects . PGS/NGS/CCS only allow us to check for gross chromosomal anomalies.
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