Should embryos developing to blastocysts on day 7 be cryopreserved and transferred an analysis of pregnancy and implantation rates

Embryos cryopreserved after reaching blastocyst stage on day 7 were compared to those cryopreserved on days 5 and 6. Day 7 blastocysts have lower but clinically important pregnancy rates.

George Kovalevsky, M.D., Stacy M. Carney, B.A., Linda S. Morrison, M.B.A., Caitlin F. Boylan, B.S., Adrienne B. Neithardt, M.D., Ronald F. Feinberg, M.D., Ph.D.

Volume 100, Issue 4, Pages 1008-1012, October 2013


To compare pregnancy rates (PRs) using blastocysts cryopreserved on day 7 with those cryopreserved ondays 5 and 6.

Retrospective observational cohort study.

Infertility center performing IVF.

Eight hundred women with infertility undergoing frozen ET.

Blastocysts cryopreserved on days 5, 6, and 7 after retrieval were thawed and transferred.

Main Outcome Measure(s):
Ongoing PRs (pregnancy developing appropriately into the second trimester). Thaw survival, implantation rates, and clinical PRs were also calculated.

A total of 1,406 embryos were thawed with a survival of 90.7% for day 5, 83.7% for day 6, and 78.7% for day 7. Implantation rates were 43.3%, 28.9%, and 28.9%, respectively. Ongoing PRs were 43.9%, 32.9%, and 26.7%, respectively.

Blastocysts cryopreserved on day 7 have a lower, but clinically important potential. Embryos that do not achieve blastocyst stage on day 6 should not be universally discarded, but should be observed in culture 1 more day as 27% may result in an ongoing pregnancy.

  • Maria Jose de los Santos

    I agree with that, in many cases we are discarding embryos that have implantation ability. We should give them the oportunity to be transferred, specially in cases where no other embryos are availble for transfer.

  • Lauren Johnson

    Thank you to the authors for describing your pregnancy outcomes with transfer of day 7 blasts in FET cycles. I agree that an ongoing pregnancy rate of 26.7% is clinically meaningful and warrants further investigation. You mentioned that among day 7 embryos that you have biopsied, the majority (67%) are aneuploidy. Do you think that there is a role for routine use of PGS prior to cryopreserving day 7 embryos?

    • George Kovalevsky

      Indeed, it appears that blastocysts cryopreserved on day 7 have a higher aneuploidy rate. We are in the process of analyzing these data. If so, it would seem that PGS would be a useful technique in this situation, especially if multiple day 7 blastocysts are available. However, we have little evidence to say that PGS will improve outcomes and thought must be given to cost efficacy. Therefore, at this point we do not routinely recommend it, but rather counsel each patient on an individual bases.

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