In an IVF cycle, embryos have to be created after an egg collection. These embryos grow until the lab decides it is time for a transfer or freeze; this is up to the clinic/doctor which day they want to do it. You may either have a transfer in the days after your egg collection; this is a FRESH transfer, or you may have your suitable embryos frozen for a future FROZEN embryo transfer (also called a Freeze All cycle).
If you are able to have a fresh transfer, you may have excess embryos which may be frozen for a future cycle, or there are just certain situations that a fresh transfer may not be appropriate.
Some reasons where a frozen transfer may be suggested:
- You stimulated too many follicles/got too many eggs
- You are at risk of hyper stimulation (OHSS)
- The endometrial lining is too thin
- Hormone levels are unsuitable for a fresh transfer, eg. premature progesterone rise
- Your embryos need to be biopsied for genetic testing and you need to await results
Where too many eggs have been collected, the body is at risk of ovarian hyper stimulation syndrome (OHSS). This can not only be dangerous after transfer, it can make a woman very unwell if pregnancy occurs. It is important to know that the uterine environment may not be suitable for an embryo in these situations and some studies suggest endometrial receptivity is decreased in a fresh cycle due to the hyper stimulation of the ovaries.
So…Fresh or Frozen?
Some labs now are doing majority frozen transfer, so you may not get the option of having a fresh transfer. One of the reasons behind this is that the body is better for receiving and embryo when the body has not just been artificially stimulated from the injections.
If the endometrial lining is good, hormones are appropriate and there isn’t any indication of hyper stimulation, then a fresh transfer may be suggested by your clinic. The embryos have not been affected by freezing and thawing, so the quality can be better, but overall, success rates are comparable. It is up to your doctor to decide if a fresh transfer is appropriate for you or if it is a better idea to freeze all suitable embryos and have one replaced in a future frozen cycle.
When embryos are frozen, they may get damaged from the freezing or thawing process, so there is a chance it may not survive. With current technologies for embryo freezing called ‘Vitrification’, survival rates are over 90%, but there are still some which don’t survive, or are damaged, but the embryos that do survive can recover well and continue their development nicely. So while many labs are turning towards frozen transfers only, it is important to know that there are slight risks involved.
While there are risks as mentioned for FETs, a frozen embryo cycle is much simpler and cheaper than an IVF cycle. The ovaries do not need to be hyperstimulated with injections and there is no egg collection. You will still get monitored for ovulation and endometrial development. You may have a natural cycle or be prescribed medication to help you ovulate as the embryo needs to go back in at the right stage of endometrial development.
The benefits of a fresh transfer is that you don’t need to wait another cycle, the embryo goes into the uterus just days after the egg collection. There is no additional cycle of monitoring with bloods and scans and there are no additional costs of another cycle (unless this cycle is unsuccessful).
So is one better than the other? No. Success rates are comparable! The right treatment for you depends on many factors and your doctor will take into account your age, history, and stimulation (among other factors) into account before making the decision of what is appropriate for you. So while you may be disappointed to be told you are not able to have a transfer after your retrieval, please know that the doctors want to do what will give you the greatest chance of success. If you have frozen embryos that you are wanting to use but worried they aren’t fresh, please know that there are many situations where a frozen transfer is necessary and success rates are just as good.
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