Q from U: Growth potential of frozen vs. fresh embryos

March 28, 2012Carole 4 Comments »

Hi Victoria,

You asked me:  Do previously cryopreserved embryos develop similarly to fresh embryos so that, if one is attempting an e-SET, growing them out is one way to determine the ‘best’ one or are they somehow more fragile?

How well thawed embryos grow out depend on several factors:

  • method of freezing and thawing (Vitrification has the potential to completely preserve the integrity of the cells meaning no cells die, if performed properly compared to slow freeze protocols in which some loss of cell viability is expected)
  • How well method was performed (Even vitrification, if done poorly, can kill some or all of the cells)
  • Both the freezing and the thawing (thawing is termed  “warming” for vit) must be done expertly. A botched freeze can’t be saved by a perfect thaw  and vice versa.
  • The culture method employed by the clinic (can they routinely grow fresh embryos to blastocyst stage- or is this problematic for them?- do they mostly transfer on day 3?), If day 5 culture is one of their strengths, go with it.
  • Intrinsic properties of the embryo (genetic or metabolic) which determine if it will continue or die

If all these factors are in your favor, it is perfectly reasonable to grow thawed embryos out in culture to see which ones can make it to blastocyst stage because these are most likely to implant. Frozen embryos shouldn’t really be more fragile once they have recovered from the freeze/thaw process. The only other alternative is to thaw one for eSET and hope for the best (that it will progress appropriately and be transferred) which is more risky than thawing several and growing them out to select for one “best”.  Good luck for a positive pregnancy!!

Related posts:

Embryo stages, progression and pregnancy outcomes

Day 3 vs. Day 5 culture

© 2012, Carole. All rights reserved.

4 Responses to this entry

  • It Is What It Is Says:

    I so appreciate this as I am nearing transfer with donated embryos set for this weekend. We have three, vitrified in one straw, that we will thaw on Friday. With our previous FET we planned for an e-SET and with one compacted morula thriving from the three that is what we got. This time, we will transfer all that are growing.
    Fingers crossed for success at this last effort.

  • Carole Says:

    Wishing you Much Good Luck!!! Carole

  • Bec Says:

    Have you found in your experience that frozen hatching blast has a lower thaw rate than a blast that has not yet hatched? I have a frozen expanded blast that is top grade and a frozen hat hung blast that is 2nd grade from top. Will be transferring top grade expanded blast in this next FET. I have been told for any subsequent FET I may require the hatching blast has a lower thaw rate due to its hatching ‘ appendage’.
    Would you agree?
    Hypothetically if both thaw well which one has greater chance of pregnancy ?
    Thanks in advance. Such a wonderful blog.

  • Carole Says:

    Hi Bec,
    Thanks for the kind words about the blog. Re: your question. In my experience with vitrification– you could get very good results with either a hatched or not hatched blastocyst. WIth vitrification, the key was to ensure that the cryopreservation medium easily and fully penetrated the embryo. For blastocysts, their stage of development determined whether they needed a single extra step before freezing. If they were fully expanded, straining at the shell but NOT YET hatched, we had to deflate them temporarily with a needle puncture or laser shot by opening up a little space between two cells. This allowed good penetration of the embryo. Hatched blasts didn’t need this; really early blasts also didn’t need this step. SO in this sense, hatched worked better than unhatched. The only problem with hatched embryos is that they are hanging out of or have completely lost their protective shell. They need to be handled with extra care as they are extra fragile– so in this sense, they might be a little more vulnerable to damage from handling during the thaw process. With a little luck and good pre-freeze preparation, either hatched or unhatched embryo should do well-= with vitrification. I am no fan of the older alternative method- slow freezing- so I can’t advise you about that. Your IVF lab team may be reporting that in their hands, they have more success with one type over the other so go with their recommendation, Good Luck!!

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