Timing of frozen embryo transfer

Dr. Beth Taylor

May 09, 2021

We all agree fresh chicken tastes better than frozen. We’ve seen popsicles get a weird coating of ice when they have been in the freezer too long. This life experience is why most people, when they initially approach embryo transfer, want a fresh embryo transfer. They do not want a freezer burnt embryo. So it often comes as a surprise to people when they learn that frozen embryo transfer pregnancy rates are generally higher than fresh embryos transfers.


This trend, along with increased use of chromosomal testing of embryos (PGT), means that at Olive nearly 90% of all embryo transfers done in the past year were frozen embryos.


The reason fresh embryo transfer pregnancy rates are typically lower than frozen is because during IVF ovarian stimulation the woman’s hormones are very high - unnaturally high or “supraphysiologic.” Such hormone levels have a negative impact on the uterine lining - where an embryo is placed. These unnaturally high hormone levels (largely estrogen) impact the stickiness or receptivity of the uterine lining.


So, for most people IVF is three months:


  • is priming or preparation
  • is ovarian stimulation, egg retrieval and embryo creation
  • is frozen embryo transfer


Now, is month #3 too soon to do the transfer? Have a woman’s hormone levels gone to a natural level by the third month? Would it be better to wait until month #4 to do the frozen embryo transfer?


A study published this month in Fertility & Sterility looked at this question. The study was performed at Cornell University and examined natural cycle frozen embryo transfer performed in the first or second month after IVF and found NO difference in pregnancy rates suggesting there is no need to wait a month after an IVF cycle.


The timing of medicated frozen embryo transfer cycles has been examined as well in previous research, and again no difference was found between the women who had an embryo transfer in the first month after IVF or second month.


At Olive most of our embryo transfer cycles are medicated. Natural cycle transfers have similar pregnancy rates to medicated if the woman is perfectly ovulatory. Medicated frozen embryo transfer cycles have the advantage of being predictable, do not require ovulation and are able to benefit from endometrial receptivity testing (ERA).


I won’t get into great detail today on natural cycle transfers versus medicated (I generally favour medicated as we can do endometrial receptivity testing (ERA) and then be much more confident we have perfect timing for the embryo transfer), but will in another blog.


The message here is that there is no need to wait a month/cycle after IVF to have a frozen embryo transfer for most women. Who SHOULD wait a cycle? Those who develop ovarian hyperstimulation syndrome (OHSS), those doing endometrial receptivity testing, and those who need uterine surgery to remove polyps/fibroids/scarring prior to a transfer.


Discuss the optimal embryo transfer timing with your doctor. Ultimately everything is personalized but do not worry about doing the transfer in the cycle right after IVF or in waiting a cycle. There is no harm nor benefit to doing the transfer right away, or waiting.


Reference: Bortoletto P, Romanski PA, Magaoay BI, Rosenwaks Z, Spandorfer SD. Time from oocyte retrieval to frozen embryo transfer in the natural cycle does not impact reproductive or neonatal outcomes. Fertil Steril. 2021 May;115(5):1232-1238.


Dr. Beth Taylor MD, FRCSC

Reproductive Endocrinology & Infertility

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