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Friday, December 14, 2012

In the past , the standard was – Transfer the best, freeze the rest ! Is a freeze all policy better today ?


In a conventional IVF cycle , usually several embryos are generated and the best looking embryos (usually a couple of embryos ) are transferred to the uterus.  The remaining embryos are frozen and are used during subsequent embryo transfer attempts. 

How is an embryo frozen ? What happens to the embryo when it is frozen ? Freezing of embryo involves the use of cryogenic temperatures (below -150°C) and cryoprotectants
( substances which are used to protect the biological materials from damage due to freezing) .  Embryos which are frozen at such cold temperatures remain without any change in their functionality or in their genetic make-up for centuries. The embryos remain ‘frozen in time’ – metabolically inactive ! The length of time an embryo is frozen will not affect its quality in anyway.

What are the methods used for freezing embryos ?

There are two methods which are widely used for freezing embryos : slow freezing and vitrification.

The older slow-freezing techniques used a lower concentration of cryoprotectants. As the name suggests, freezing is achieved slowly, in a step-by-step manner and such programmed cooling requires costly instruments which could cool the embryos steadily by maintaining appropriate temperatures. It is also a time-consuming process and this technique doesn’t prevent the formation of ice crystals in embryos. These ice crystal can kill the embryo during freezing and thawing, as a result of which their survival rate was never optimal.

Vitrification is a technique in which the cells are cooled ultrarapidly (at an extremely high cooling rate) . It needs a much higher concentration of cryoprotectants. The advantage of vitrification is that ice crystal formation within the cells is totally prevented. It transforms the cytoplasm within the cells into an amorphous glassy state. This technique doesn’t need expensive equipment; but does require experience and expertise.

Which embryo freezing technique is the best ?

Scientific studies have showed that vitrifying embryos resulted in better embryo survival after thawing. Vitrified embryos also had a much higher proportion of intact blastomeres (individual cells of cleavage stage embryos) when compared to embryos frozen using slow freezing technique. The post-warming morphology of the embryos is excellent and the pregnancy rate and implantation rate is found to be better with vitrified embryos. All these beneficial effects are attributed to the lack of ice crystal formation in vitrified embryos which in turn prevents injuries due to ice formation. Hence vitrification is the current preferred method of freezing embryos in most IVF clinics world-wide.

Why is embryo freezing important ?

Freezing embryos helps in utilizing the extra embryos produced during an IVF cycle in an efficient manner and hence the need for discarding supernumerary embryos is prevented.  When an embryo is discarded a life that might have the potential to develop into a full-fledged baby is lost. Since we still do not have accurate technology to pinpoint which embryo will develop into a baby, discarding human embryos becomes an ethical issue. Embryo freezing helps in addressing this ethical issue effectively. Freezing embryos also alleviates the need for further ovarian stimulation cycles when an embryo transfer attempt fails. Hence the financial and physical distress associated with a new IVF cycle is circumvented. The success rate of an IVF cycle naturally increases when there are many frozen embryos available since many more embryo transfer attempts could be made.

Is a fresh embryo transfer better than frozen embryo transfer ?

Before the introduction of vitrification for human embryo freezing, fresh embryo transfer had a higher success rate. With the introduction of vitrification , this scenario has changed dramatically.  When embryos are vitrified , the success rate of a frozen embryo transfer is equal to that of a fresh embryo transfer - or is even higher. Hence the statement ‘ Transfer the best, freeze the rest’ is no longer valid today !

Why is a frozen embryo transfer better than a fresh embryo transfer in terms of IVF success rates ?

1)  Vitrification for embryo freezing has led to a better survival rate of post-thawed embryos ; in good clinics, the survival is nearly 100% , and not a single blastomere is lost as a result of the freezing and   thawing.
2)  The endometrial receptivity is found to be excellent during a frozen embryo transfer cycle. During an IVF stimulation cycle (fresh cycle) the estrogen level in the body rises too high and such high estrogen levels are shown to be deleterious for optimal endometrial receptivity. A FET simulates a better and more natural endometrial environment when compared to a fresh IVF cycle. Embryo-endometrial synchrony can also be better achieved in a FET cycle.

If this is so, then is a freeze all policy better today ?

The data from randomised trials favour frozen embryo transfer as compared to a fresh embryo transfer (although larger trials are needed to confirm these results). Kato clinic in Japan , which does about 10000 cycles per year , performs only FET for all its patients and their reported success rate is very high ! It’s high time that all the IVF clinics and patients think of freezing all the embryos obtained during an IVF cycle and transfer them sequentially so that the chance of achieving a pregnancy increases. Apart from the positive aspects of FET described above , there is one more valid reason for opting to do a frozen embryo transfer. We still do not have a valid, fool-proof technique to determine which embryo has the potential to develop into a baby. Embryos which are selected to be transferred to the uterus using microscopic morphological criteria fail to achieve a viable pregnancy many a time. Many good looking embryos fail to implant  and many poor looking embryos do turn into a much desired baby. In such a situation, freezing all the embryos and transferring them sequentially might improve the odds of pregnancy when undergoing an IVF cycle.

Hence a freeze all policy is definitely a better option today and FET will soon replace fresh embryo transfer in the near future !

So if your fresh embryo transfer did not work, do not panic. A frozen embryo transfer is no less efficient than a fresh embryo transfer. Before starting an IVF cycle it is important for you to make sure that the IVF clinic you select has an embryo freezing facility - and , more importantly , that they use the vitrification technique for embryo freezing.


  1. Very informative, Manju. It makes sense to me now why frozen embryo transfers were statistically less likely to lead to pregnancy, given that the best were transferred first. However, I'm still not clear as to the mechanism responsible for vitrified embryos doing better than embryos that were never frozen to begin with. So are you recommending they be flash frozen and then implanted, even if you have no need to implant any at a later date? That would akin to flash freezing fresh bread dough, thawing it, and then cooking.

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  4. Dana nice to meet you : ) I think I didn't do a good job. Now I will try :

    For example a woman has 15 embryos - 2 were transferred in the fresh cycle. It didn't result in a pregnancy. If her embryos were frozen using slow-freezing method her chance of achieving a pregnancy is higher in a fresh cycle when compared to a frozen cycle because slow frozen embryos are more likely to get damaged while thawing and hence their developmental potential is impaired (hence implantation is affected too!). But if her embryos are frozen using vitrification, her chance of achieving a pregnancy with those vitrified embryos is as high as the fresh cycle (or even more) because her embryos are less likely to be damaged during thawing. In my clinic they have a 100 % thaw rate - it means they are able to thaw my embryos without even losing a single cell from the embryo (all the cells in the embryo are intact after thawing). Such vitrified embryo's implantation potential is thought to be higher than slow-frozen ones.

    The next is embryo quality - a women got only 5 embryos and they transferred the three best looking embryos in the fresh cycle. She is left with only two not so good looking embryos which are frozen. Even if the poor looking embryos are vitrified her chance of success may be compromised in the subsequent frozen embryo transfer, because her embryo quality is poor (even if the embryos are thawed successfully without damage !) But you should remember that even worse looking embryos can give rise to beautiful babies (genetically normal embryos can look worse under the microscope and genetically defective ones can look beautiful as well !). That is why it is good to freeze even the bad looking ones and when doing so vitrification technique is the best.

    Another thing here is endometrial receptivity - studies show that in a fresh cycle due to the presence of high estrogen in the body the endometrial receptivity is compromised. Before vitrification technique was introduced even though this endometrium receptivity is a negative point in fresh embryo transfer, slow-freezing of embryos compromised the success of an embryo transfer more than the poor endometrial receptivity of a fresh cycle would. So fresh cycle was thought to be better.

    Now we have vitrification technique where the embryos could be thawed without damage. And in fresh cycle there is a danger of the presence of less receptive endometrium. So to circumvent poor endometrial receptivity, if all the embryos obtained during a fresh cycle are frozen (especially when there are only a few embryos available!) using vitrification and then transferred sequentially to the uterus (which now has a better receptivity when compared to fresh transfer!) the chance of achieving pregnancy may be higher. That is why some clinics have high success rate with a frozen embryo transfer than a fresh embryo transfer now-a-days. Perhaps in the future everyone will resort to frozen embryo transfer because the endometrial receptivity seems to be better in a frozen cycle than a fresh cycle and the vitrified embryos fare as good as fresh embryos.

    I hope this explanation helps you. If you have further doubts please write to me.


  5. Ah, that's what I suspected. Being able to marginalize or eliminate the negative effects of slow freezing allows implantation at an ideal time, rather than hurried along at some (possibly problematic) interval. This is Demian form the IVF forum, by the way. My wife and I both have "pen names" on the internet because people tend to look at her name and think she's a man and they tend to look at my name and think I'm a woman! Anyway, I'm enjoying the blog.

    I was curious about your opinion on some other matter. Our doctor has a very good reputation and high success rate, but my wife and I are torn on one of his recommendations: acupuncture. We're both "show me the evidence" kind of people and most of the literature I've seen on acupuncture is somewhat dubious, with one or two articles that may have methodological issues. I know that acupuncture probably has a pretty robust placebo effect, but if you don't "believe" that it works, then your out of luck! It seems kind of arrogant to go against the recommendations of the doctor, but I'm pretty sure my wife's "chi" is doing just fine. What do you think.

  6. Demian, nice to hear from you ! I am happy that you are enjoying my blog.

    I do not believe acupuncture could help in improving embryo quality or embryo implantation. As you have rightly said - there is no scientific proof. What makes me uncomfortable is; IVF patients are many a time mislead with false promises about such alternative therapy's effectiveness. I am happy if people understand that such therapies can help one to relax and increase a sense of general well-being - nothing more !

    My stand is - if something can help you to feel better physically and mentally among the most stressful IVF journey give it a try provided it doesn't cost you a fortune and if it doesn't harm you.

    So, why doctors advise such therapies ? When patient's ask what can be done to improve my success or why did my cycle fail - they are forced to give an answer ! The only honest answer is 'repeat the IVF until you succeed' !


  7. Yeah, I think you are right. Perceiving that something "extra" is being done to improve your odds can reduce stress, anxiety, etc. I can see where acupuncture might conceivably relieve pain at a specific source, but I cannot conceive of a mechanism that would actually improve egg/embryo quality. I've been told that acupuncture apparently "improves blood flow to the uterine lining" but I'm still skeptical. Thanks for the advice! Also, my google account is being a bit wonky, so if you see any double posts, go ahead and delete one.

  8. Hi Manju..

    I am 29 years old and have faced one failed FET. Before transfer, embryos had 8 and 7 cells but after thawing cells reduced to 6 and 5 respectively. Doctor claimed that they used vitrification process. I wanted your opinion. What could be the reason of failure? were the embryos of poor quality before freezing or they become inferior due to poor freezing expertise/ technique or you think there might be some other reason. I suffer tubal factor infertility due to tuberculosis infection in the past. I have heard ivf is generally a success with tubal problems, then why did the cycle failed.?
    Also my AMH in May 2013 was 1.24 . Doctor has put me on 75 mg DHEA for two months before next cycle. Do you think only 2 months of DHEA can work? I am nervous to under go another cycle in December because of fear of failure. How should i prepare for it? any advice from some one like you who has seen so much in life would be appreciated.

    1. Dear commenter,

      I am sorry for not replying early enough.

      Can you give me more details ? How many eggs were retrieved from you during your IVF cycle ? How many embryos you got ?

      Your AMH value is low although not that low. If you got only few eggs with high dose of gonal f it does confirm that you have low ovarian reserve. This could be one reason for poor embryo quality.

      Please mail me : manjupadmasekar @ I would be able to help better if you could give more details.

      I understand your fear but unfortunately nothing much can be done. Eat well, relax, have realistic hopes, make sure your thyroid is normal.


  9. Hi manju..
    Thanks for the reply. I know the difficult time u r facing so i dont mind delay in your reply. your reply itself was important, not the timing. Will mail u more details very soon!!

    thanks again and do take care..


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