Developmental potential of slow-developing embryos: day-5 morulae compared with day-5 cavitating morulae

Transfer of fresh slow-developing embryos seems to improve the cycle outcomes compared with culturing for another day and then vitrifying and thawing later.

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Volume 111, Issue 1, Pages 105–111


Jigal Haas, M.D., Jim Meriano, M.A., Rawad Bassil, M.D., Eran Barzilay, Ph.D., Eran Zilberberg, M.D., Robert F. Casper, M.D.



To describe and compare the ongoing pregnancy rate between morulae and cavitating morulae (CAVM) transferred on day 5, to describe and compare the blastulation rate between day 5 morulae and CAVM, and to describe the pregnancy rate of these slow-developing blastocysts during a frozen embryo transfer (FET) cycle.


Retrospective cohort study.


Single tertiary care medical center.


Delayed-development embryos: 3,321 cycles that included 10,304 embryos on day 5 that were cultured until day 6.


Development of morula and CAVM to the blastocyst stage.

Main Outcome Measure(s)

Blastulation rate.


The fresh embryo transfers comprised 186 patients with 82 embryos at the morula stage and 104 embryos at the CAVM stage. The pregnancy rate (15.8% vs. 21.1%) and the ongoing pregnancy rate (15.8% vs. 17.3%) were comparable between the groups. The study group included 10,304 day-5 delayed embryos: 5,395 morulae and 4,909 CAVM on day 5. The blastulation rate was statistically significantly higher in the CAVM group compared with the morula group (39.2% vs. 20.4%). We included 201 FET cycles: 77 warmed blastocysts that developed from a morula on day 5 and 124 warmed blastocysts that developed from CAVM on day 5. The clinical pregnancy rate was comparable between the two groups per embryo transfer (21.3% vs. 24.7%).


Transferring of fresh, slow-developing embryos seems to improve the cycle outcomes compared with culturing for another day and then vitrifying and thawing later.

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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. The journal publishes juried original scientific articles in clinical and laboratory research relevant to reproductive endocrinology, urology, andrology, physiology, immunology, genetics, contraception, and menopause. Fertility and Sterility® encourages and supports meaningful basic and clinical research, and facilitates and promotes excellence in professional education, in the field of reproductive medicine.


Go to the profile of Liu CH
about 2 years ago

Would  authors  kndly comment on the very different conclusions in the article by Tannus( Human Reproduction, Vol.34, No.1 pp. 44–51, 2019) with similar topic by different design?