Saturday, November 14, 2015

Why Frozen Thaw Embryo Transfer has Better Success Rates as compared to Fresh Embryo Transfers

Why Frozen Thaw Embryo Transfer has Better Success Rates as compared to Fresh Embryo Transfers
Dr. Sai, Chief Embryologist , Malpani Infertility Clinic Pvt. Ltd.

We often see that patients, who fail to get pregnant in their first cycle with Fresh Embryos, get pregnant in their very next Frozen Thawed Embryo transfer. This is surprising, because we choose the  best-quality embryos for your fresh transfer. So why are the results better with your Frozen Embryos ?

Our success rate in Frozen Thawed Embryo transfers at Malpani Infertility clinic is 62 % as compared to  46 % with a Fresh Embryo Transfer. This is because the Implantation rate is better in a Frozen Thawed Embryo transfer cycle, as compared to a Fresh Embryo Transfer. Let's see why this is so.

Implantation represents one of the important steps for the success of assisted reproduction
techniques (ART)

Its effectiveness relies on three variables:
•    Embryo quality,
•    Endometrial Receptivity (ER), and
•    A well-balanced Embryo-Endometrium interaction

The implantation window is a self-limited time period in which the endometrium has acquired the characteristics to allow for attachment of the blastocyst. This is why optimal, Endometrial Receptivity (ER) is essential for conception in both natural and infertility treatment cycles.

Endometrial Receptivity (ER) is Better in Frozen Thawed Embryo Transfer Cycles

The problem is that in a fresh cycle, the superovulation or controlled ovarian hyperstimulation (COH) we use to help you grow lots of eggs adversely affects endometrial receptivity. This is because of the excessively high levels of estradiol (E2 ) and progesterone (P) during the fresh IVF cycle, which leads to biochemical endometrial alterations. Ultimately, these physiologic changes may affect the success rates of the treatments. These altered hormone levels could mediate an asynchrony between the endometrium and the transferred embryos, leading to an endometrial environment that could be responsible for implantation failure.

The reason for a higher Pregnancy Rate in Your Frozen Thawed Embryo Transfer Cycles is that your endometrium is artificially primed with the use of estradiol (E2 ) and progesterone (P) and the embryos are therefore transferred to an environment that had not suffered the effects of the supraphysiologic hormonal levels that occur during Controlled ovarian hyperstimulation COH.
The endometrial development can be controlled more precisely in a frozen cycle.

Embryo Quality (Frozen Embryos are as good as Fresh)

The quality of the frozen embryos , and their potential to implant is exactly the same as fresh embryos, thanks to advances in embryo cryopreservation technique.  Vitrification ( flash freezing) has been a blessing for all of us, and is the preferred technique for cryopreservation of Embryos worldwide.
Vitrification is the modern, efficient and effective manner to freeze your embryos as opposed to the conventional method of slow-freezing.
Vitrification allows us to freeze your embryos in a glass-like state , to avoid ice-crystal formation associated with freezing. In this manner, damage to your embryo is prevented, and the integrity of the embryo is preserved. Vitrified embryos may be stored indefinitely.

Before Freezing                                                                                 
    After Thawing

As you can see from the above images, it's impossible to make out which embryo is fresh and which one has been thawed after freezing it for 1 year.

However, it is true that the vitrification technique is difficult to master and involves a steep learning curve. Not all IVF clinics will have such good results. We have now frozen  over thousands of embryos, and have a  nearly 100% survival after thawing.

How freezing your Embryos improve your chances of Conception

Patients get upset when we do not transfer their fresh embryos in their IVF cycle. After all, if we do not transfer, then how will they get pregnant. However, the short-term distress this causes is more than compensated by the higher pregnancy rates we achieve with this policy. If we freeze all your embryos , we can save best embryos for Frozen Thawed Embryo Transfer (FTET) and with the improved Endometrial Reseptivity (ER) in the FTET cycle, your chances of conception can be as high as 80% if we have 4 blastocysts. This is because we transfer only 1-2 blastocysts per cycle, which means we can do 1-4 frozen transfer  for you, thus dramatically improving your cumulative conception rate.

We prefer to  freeze all your embryos (if we get more than 15 eggs) to completely eliminate your risk of ovarian hyperstimulation syndrome (OHSS) . We can then transfer your best Embryos in your subsequent FTET cycle

Advantages of Doing a Frozen Thawed embryo Transfer over Fresh Embryo Transfer

•    Preventing/ Eliminating late- onset OHSS
•    Allowing time for genetic testing ( for patients who need PGD)
•    Restoring endometrial receptivity , thus increasing the implantation and pregnancy rates

Need help in getting pregnant ? Please send me your medical details by filling in the form at so that I can guide you !


  1. Anonymous7:28 PM

    Can the better implantation rate during FET be due to the fact that women who have embryos to freeze naturally have a higher chance of having better quality embryos and hence higher chance of implantation? For example, if you consider all the fresh cycles, you will include both category of women -women who have embryos to freeze, and women who don't. Do women who have embryos to freeze have better pregnancy chances? When it comes to FET, only women who produced enough embryos to freeze are taken into account when calculating pregnancy rate. How can this bias be explained? Only when embryos of all women are frozen and FET cycle is performed, the pregnancy rate calculation is justified. Do surrogacy cycles have higher implantation rates?

  2. Yes, surrogacy cycles; donor egg cycles ; and donor embryo cycles , all have higher pregnancy rates, as compared to fresh IVF cycles


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