Does Frozen Embryo Transfer (FET) Improve IVF Success?

“I am in full agreement with researchers at Cambridge University in the United Kingdom who following a recent published a report on their observation that FET enhances IVF outcome, stated that this could represent one of the most “exciting” IVF revelations of the last  25 years.”

I am often asked by patients whether there is a benefit in doing frozen embryo transfers over fresh embryo transfers and how this decision impacts IVF outcome. Women undergoing IVF usually have one or more fresh embryos transferred within a week of their eggs being harvested following ovarian stimulation with fertility drugs

I have long held that, provided embryos are frozen in their most advanced (blastocyst) stage of development,  that freezing is effected using ultra-rapid vitrification (rather than using previous slow-freezing methods) and optimal technique is employed during the performance of the freezing process, that Frozen Embryo Transfer (FET) will not compromise IVF outcome. It has been my expressed position that while this benefit is least apparent in younger women (<35y) and those who have normal ovarian reserve, it quite profound when it comes to older women , women who have Diminished Ovarian Reserve (DOR) and women with Polycystic Ovarian Syndrome (PCOS). It is my opinion that this is largely attributable to the fact that the ovaries of the latter group of women have a tendency to over-produce  male hormones (androgens) such as androstenedione and testosterone which reach the ovarian follicles in excess , compromising egg development and maturation thereby  increasing the incidence of egg numerical chromosomal irregularities during meiosis (maturational division) and diminishing the  “competency” to produce viable embryos following fertilization.

A recent study reported from Cambridge in the United Kingdom has now confirmed this observation, reporting a roughly 50% improvement per embryo transferred following FET as compared with fresh embryo transfers.

The reason for the improvement in IVF outcome following FET obviously has little to do with any direct influence of freezing on embryo competency. Rather, it likely is due to targeted and measured hormonal manipulation in preparation for FET improving optimize endometrial receptivity. This likely also serves to explain why older women, women with DOR and those who are high responders (e.g. PCOS) and accordingly have dysfunctional ovarian hormonal production in response to ovarian stimulation with fertility drugs are the ones who are most likely to benefit from more programmed endometrial development.

Regardless however, it should be pointed out that this new revelation showing that FET can only enhance IVF results, should be comforting to those women undergoing FET for other established indications such as: preimplantation genetic testing (PGT) and/or Preimplantation Genetic Diagnosis (PGD), both of which preclude performing embryo transfer in the same cycle as the egg retrieval and  for other embryo recipient situations such as egg donor-IVF, Gestational Surrogacy (GS) and  Embryo Adoption (EA).


Lauren S

Hi Dr. Sher,
I just completed a mock FET cycle and planning on doing the real FET next month. My lining the day before the simulated transfer day was 8.9 mm (after 13 days of estrogen). On the actual mock embryo transfer day, my E2 level was 137 and my Progesterone level was 23 (after 5 days of PIO). Are my E2 and Progesterone levels optimum for implantation? I have read a couple of articles where they have stated a progesterone level over 20 is not good?

Dr. Geoffrey Sher

It all depends on what delivery system of estrogen was used (parenteral, oral, trans-dermal or vaginal).

Geoff Sher


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