Embryo Slow division and fragmentation
3 Replies
Brenda - December 13

Hi Dr. Smith
I have a questions regarding the embryos slow division cycle and fragmentation. Why do some embryos divide well but have poor fragmentation?

Can an embryo have slow division and not poor fragmentation?

Does the cytomoplasmic part of the egg generate the energy for the embryo upto day 2 and then on day 3 does the sperm contribute to this energy to help the embryos to continue to divide to the morula stage or day 5 stage.
On day 5 should the embryo only be at the morula stage and not the blastocysts stage.

Success rates for an ivf cycle, is it based on the grade and quality** per embryos**, is that how the total success of the potential outcome is determined by adding the success rates per embryo for the total potential of outcomes for any given transfer?

ON a frozen donor egg thaw, if three embryos are thawed is the potential of success depended on the grade and cells of the individual embryos and then those totals are added to gether for the ***total** potential of the cycle?

are there studies that have been conducted on individual embryos grade and cell division that gives these odds per embryo?

what are the unknowns of embryo development at day 3 and at day5?


Dr Smith - December 19

Heavily fragmented embryos (>20% fragmentation) rarely divide beyond the 8-cell stage, so they only divide "well" up to a point.

Yes, an embryo can have a slow division without significant fragmentation. Some embryos with slower division cycles are destined to become blastocysts on Day 6 of development. However, most embryos with slow division cycles and minimal fragmentation do not grow beyond the 8-cell stage.

The egg cytoplasm is responsible for carrying the embryo through the first 2 division cycles (to the 4-cell stage) without additional genetic instructions from the nucleus/nuclei of the embryonic cells. However, if the embryo is going to develop beyond the 8-cell stage, additional genetic instructions from both the sperm DNA and the egg DNA are required. This is a process called "activation of the embryonic genome". If this process is unsuccessful (due to genetic problems in the sperm, egg or both), the embryo usually arrests between the 4 and 8-cell stage.

Embryos with the best developmental potential reach the morula stage on Day 4 and the blastocyst stage on Day 5. However, embryos that reach the morula stage on Day 5 and the blastocyst stage on Day 6 also have reasonable developmental potential.

The official measure for success rates in the U.S. is the percentage of cycles resulting in a live birth. This rate does not take into account the number or quality of embryos transferred or the day of transfer. It also does not take into account the type of gestation (single, twin, triplet, etc). Accordingly, there is no incentive to reduce the number of embryos transferred to reduce high order multiple gestations. This is stark contrast to other countries that put a strict limit on the number of embryos that may be transferred.

The FET success rate is measured in the same way as the "fresh" cycle. If one is going to try to predict the potential outcome, one would factor in the number of embryos transferred, their cell number and grade. There is no hard and fast formula for calculating the potential outcome, therefore any prediction of outcome should be treated interpreted with caution.

It is always difficult to predict success on a per embryo basis because we often transfer more than one embryo and the embryos are at different cell stages and of different grades. Yes, there are good studies that have controlled for these variables, but not very many of them. Unfortunately, they are now outdated and no longer predictive.

On Day 3 it is usually unknown whether or not the embryo will develop beyond the 8-cell stage. About 70% of the embryos at the 8-cell stage on Day 3 continue to the blastocyst stage, 30% do not. Embryos that have not reached the 8-cell stage on Day 3 have a significantly lower chance of reaching the blastocyst stage.

By Day 5, the mystery is gone. It is clear which embryos have reached the blastocyst stage and which have not. Embryos must reach the blastocyst stage in order to attach and implant in the uterine wall. What reamins unknown at this point is whether or not implantation will occur following embryo transfer.


jacqueline - January 22

hi, i just posted a message about speed of cell division, and wonder if you might answer this (it was in the good eggs but slow embryos)

many thanks

jacqueline (new to the message boards)


Dr Smith - January 23

I found it. Your answer has been posted.



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