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.

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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.

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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility┬« is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders.