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Frozen Embryo Transfer (FET) versus “Fresh” ET: How to Make the Decision

by Dr. Geoffrey Sher on May 24, 2016

Until less than a decade ago, most women undergoing IVF would have their embryos transferred to the uterus in the same cycle that the egg retrieval was performed (“Fresh” Embryo Transfer). This was because embryo cryopreservation (freezing) was a hazardous undertaking. In fact it resulted in about 30% not surviving the freezing process and those that did, having about one half the potential of “fresh embryos to implant and propagate a viable pregnancy. The main reason for the high attrition rate associated with embryo cryopreservation is that the “conventional” freezing” process that was done slowly and this resulted in ice forming within the embryo’s cells, damaging or destroying them. The recent introduction of an ultra-rapid cryopreservation process, known as vitrification, freezes the embryos rapidly so as to avoid ice crystals from developing. As a result, >90% survive the freeze/thaw process in as good of a condition as they were prior to being frozen without compromising in their ability to propagate a viable pregnancy.

Recently, there have been several articles that have appeared in the literature suggesting that an altered hormonal environment may be the reason for this effect. There have also been reports showing that when singletons (pregnancy with one baby) conceived naturally are compared to singletons conceived through a “fresh” embryo transfers they tend to have a greater chance of low birth weight/prematurity. This difference was not observed in babies born following FET.  Hence, there is a suspicion that the altered hormonal environment during the fresh cycle may be the causative factor.

Available evidence suggests that FET (of pre-vitrified blastocysts) is at least as successful as is the transfer of “fresh” embryos and might even have the edge. The reason for this is certainly unlikely to have anything to do with the freezing process itself. The reason likely has to do with being able to better able to prepare the uterus optimally for embryo implantation by using targeted hormone replacement therapy that when a “fresh” transfer is performed immediately following ovarian stimulation with fertility drugs.

There are additional factors other than method used for embryo cryopreservation that influence outcome following FET. These include

  • An emerging trend towards selective transferring only advanced (day 5-6) embryos (blastocysts).
  • (PGS) to allow for the selective transfer of genetic competent (euploid) embryos
  • Addressing underlying causes of implantation dysfunction (anatomical and immunologic uterine factors) and
  • Exclusive use of ultrasound guidance for delivery of embryos transferred to the uterus.

Against this background, the use of FET has several decided advantages:

  • The ability to cryostore surplus embryos left over after fresh embryo transfer
  • The ability to safely hold embryos over for subsequent transfer in a later frozen embryo transfer (FET) cycle (i.e. Staggered IVF) in cases where:


  • In cases where ovarian hyperstimulation increases the risk of life-endangering complications associated with critically severe ovarian hyperstimulation syndrome (OHSS).
  • The ability to store embryos in cases of IVF with third party parenting (Egg Donation; Gestational Surrogacy and Embryo donation) and so improve convenience for those couples seeking such services.
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  • Cristina - March 7, 2017 reply

    Good afternoon. Recently I had my first DE fresh IVF, with BFN. I am supposed to do a FET right away, however my period is late 10 days and I am worried that this show that a FET right away will not be successful. What do you suggest, is it ok to proceed with the FET, once my period arrives or better to wait the second one? Thank you!

    Dr. Geoffrey Sher

    Dr. Geoffrey Sher - March 7, 2017 reply

    I see no reason that once a period arrives you could not proceed directly.

    Geoff Sher

  • Laura - June 22, 2016 reply

    Hi Dr. Sher – I am a 37 yo woman currently being treated at SHER NYC. I recently had my first unsuccessful IVF (no IUI or other treatment prior to IVF- transferred embryo was “excellent” quality 5 day blast, lining was 8.1). We have three frozen embryos (2 excellent, one good) from that first cycle and will be doing a medicated FET after one cycle off. My question is whether you think an endometrial scratch would be worth exploring before the FET? Thank you, Laura

    Dr. Geoffrey Sher

    Dr. Geoffrey Sher - June 22, 2016 reply

    Respectfully Laura,

    I do not believe that the endometrial “scratch” procedure has proven merit.

    Geoff Sher

    Laura - June 23, 2016 reply

    Thank you for your response! Anything that you think I should be doing/exploring in advance of the FET to put me in the best possible position for success?

    Dr. Geoffrey Sher

    Dr. Geoffrey Sher - June 23, 2016 reply

    Healthy diet, some supplementation with prenatal vitamins and as much mental and physical rest as plausible.

    Geoff sher

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