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When embryos are frozen at the 2PN stage, they are at approximately 18-20 hours of development. When they are thawed, they need a couple of hours to reorganized before continuing development. After thawing, the embryos were allowed an additional 43 hours to develop. If we add up the hours (20-2+43=61), the embryos were at approximately 61 hours of development. At 61 hours, the embryos should be at the 4 cell stage of development. The embryos would not divide again to reach the 8-cell stage until around 70-72 hours of development, so there was nothing wrong with the embryos that were transferred (i.e. they weren't slow). They were developing on schedule.

Best of luck.

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Dr. Smith
Thank you for the informative information regarding the 2pn embryos and their development.

I do have another question, bc now i have a very good idea on what to expect on day 3, that the embryos will only be a 4 cell embryo.

when looking at these embryos, what time frame would a determination be made to determine if these embryos could go to blastocysts. Would it be at the 61 hour and what parameters determine if you can take an embryo to blastocysts, like how fast the cells divide?
The donor was very young and other pregnancies were created from this donor.

thanks again, soo very much.

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Unfortunately there is no sure way to predict blastocyst development on Day 2-3 (i.e. 61 hours post-thaw). The only way to know for sure is to wait and see if the embryos develop to the blastocyst stage. The most common point for arrested development is between the 4 and 8-cell stage. Even in donor egg cases, we expect that one half to the embryos will stop growing at this point. Since the embryos were transferred prior to the completion of the 4 to 8-cell transition, it is impossible to determine the liklihood of blastocyst development. In an ideal world, the embryos would have been cultured to the blastocyst stage prior to transfer.

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