Q from U: Is thawing and refreezing embryos harmful to the embryo?

October 27, 2013Carole 51 Comments »

This question came from a reader the other day:

Hi!  I think this would make a great discussion topic. It certainly interests me. My husband and I have 7 frozen early blasts (3 @ 2AA, 1 @ 2AB, 3 @ 2BB). In a perfect world we’d like to do a complete chromosomal screening on them to find which ones are euploid. My RE says this is possible and the embryologist would thaw, biopsy and re-vitrify them. She states the lab has had a lot if success doing this.My concern is for the damage to the embryos. How good are labs at doing this?  What is the general rate of failure?

The short answer is yes, particularly with the newer method of vitrification is used (as opposed to older slow freezing methods), embryo quality seems to be preserved after at least one round of refreezing. In my own lab in Indy, we found ourselves  in the position of having to refreeze when we thawed more than we needed because we assumed fewer embryos would survive.  This happened quite a bit as we transitioned from using slow freeze to vitrification because slow freeze had taught us to have very low expectations regarding embryo quality after thaw. A good thaw in the old days of slow freeze was if more than half the cells in the embryo were intact. That was pretty sad. With vitrificatiom, we saw embryos that looked the same post-thaw as they did when they were fresh. This was very exciting but we had to adjust the numbers of embryos we thawed to get just enough for transfer. We found that we also had pregnancies from twice frozen-twice thawed embryos at any stage, when we used vitrification.

Anecdotal reports such as this one can also be found in the literature:

Live birth of a normal healthy baby after a frozen embryo transfer with blastocysts that were frozen and thawed twice.Fertil Steril. 2005 Jan;83(1):198-200.

This is a report on the birth of a normal, healthy baby after embryo transfer using blastocysts that have been twice frozen and twice thawed. Eight frozen blastocysts were thawed for a frozen embryo transfer. One blastocyst was transferred to the uterus and four of the thawed blastocysts were refrozen. The patient became pregnant but suffered a miscarriage at 7 weeks. The four remaining blastocysts were re-thawed and all four transferred. The second transfer resulted in a healthy singleton birth at 38 weeks.

Here’s a much larger study that looked at the same question in 49 IVF cases.

The efficacy of the transfer of twice frozen-thawed embryos with the vitrification method. Fertil Steril. 2009 Feb;91(2):383-6. doi: 10.1016/j.fertnstert.2007.11.079. Epub 2008 Mar 4. 

This retrospective study in a private fertility clinic  looked at outcomes from 49 women who had excess embryos refrozen. These women had embryos thawed for a frozen embryo transfer cycle, some of which remained as excess embryos. The embryos remaining after the transfer were refrozen and re-thawed in a future frozen embryo transfer cycle. The pregnancy rates and implantation rates between those embryo that had undergone one freeze-thaw versus two freeze-thaw cycles were compared. Implantation rates and pregnancy rates were similar (no statistical difference) in the two groups. Vitrification was the freezing method used.

These studies only involve refreezing and re-thawing so you might well ask–Does biopsying the embryos before refreezing make the embryos less able to survive -quality intact- through a second round of refreezing?

Here’s a mouse study that looks at that question:

Refreezing of murine intact and biopsied embryos by rapid-freezing procedure. Hum Reprod. 2000 Dec;15(12):2577-81.  

The advantage of mouse studies is that you can collect a lot of data in a short period of time, This study looked at how 860 mouse embryos fared after freezing , thawing with or without biopsy, then refreezing and re-thawing. They looked at the implantation and pregnancy rates of mice who had a transfer with these embryos. The bottom line is that the implantation, pregnancy and live birth rates were not statistically different between those embryos with the fewest interventions and those with the most.

With the advent of genetic screening of biopsied embryos, which based on the last ASRM meeting, is becoming more and more widespread in US clinics, the freezing of blastocysts is becoming routine after biopsy and results are good with thawing of these once-frozen blastocysts. Because other patients who have untested frozen blastocysts in storage will likewise wonder if they might benefit from genetic testing which – in their case–would require  thawing for biopsy, then refreezing to save embryos pending genetic test results. So having twice-frozen twice-thawed embryos for embryo transfer will likely become more common.  I haven’t been able to find any studies with large numbers because we just haven’t collected (or reported) the data yet beyond anecdotal reports of a small number of patients in clinics. And of course, it will take even longer to have any long-term outcome data on the health of these kids born from twice-frozen, twice-thawed, biopsied embryos.

Bottom-line. I have every reason to think that this can work and result in good outcomes in terms of pregnancy and live birth rates– longer term outcomes are unknown based on no long-term data. However, as with every intervention in the IVF lab, it can be done poorly or well. Keep in mind, for this to work, freezing, thawing and biopsy must be done with a high level of skill multiple times on the embryo. Highly skilled ART techs can do this. Poorly trained techs in labs that rush to meet consumer demand for either vitrification or biopsy or genetic testing without adequate training won’t be able to pull this off. So as usual, the questions to ask your program are:

How many times have you performed this intervention (biospy and refreezing followed by an FET)?

What data do you have on outcomes from this approach? Implantation rate, pregnancy rate and live birth rate.

The reader who asked this question shared that her RE told them they have a lot of success with this. Great! Then they shouldn’t mind sharing numbers. What’s does a “lot of success” look like in actual data?

If you are the first patient for any new intervention, you have no information to go on and your risk of a poor outcome is not calculable. If there is data, you’ll have a better idea of whether the risk of exposing your embryos to repeated interventions is worth it in terms of possible benefit (information about the genetic status of your embryo). The key is getting enough information as possible about risks, benefits and alternatives before you agree to any medical intervention.



© 2013, Carole. All rights reserved.

51 Responses to this entry

  • Milky Says:

    Hi I’m glad I found this blog and read the whole article and comments. Not sure if you are still checking the comments or not though 🙂 Btw I was searching ‘Refreeze embryos’ cases specifically without PGS. I just finished eggs retrieval, total 19 and it ended up 2 of D3 embryos and 4 blastocysts all frozen. By mis communicating with my clinic, they free my embies in pair, however I planned to do single embryo transfer (SET) only. And my embryologist said it’s not a problem to thaw two embryos together, transfer one and the rest can be re-frozen. I’m wondering if it’s really safe to do so. (I’m not sure which technic my clinic uses to free/thaw, but they mentioned when it’s re-freeze embryos, damage is extremely minimal) Your article is about the safety of thawed-biopsy-refreeze-transfer, and if there’s no biopsy included, is it even more safer to refreeze and rethawing? Thanks a lot.

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