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Egg Grading


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#1 want2

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Posted 22 July 2008 - 10:17 PM

What is the difference in grading between m1 and m2 eggs retrieved....?thanks

#2 Geoffrey Sher, MD

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Posted 23 July 2008 - 07:47 AM

An M1 egg has not yet gone through Meiotic division and has all 46 chromosomes present. An M2 egg has...and has halved its chromosomes to 23 in readiness for fertilization.

Geoff Sher

#3 want2

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Posted 23 July 2008 - 08:39 AM

So would I assume an M1 would not accompany the m2 's to the lab for cgh testing? is it possible to mature the m1's in vitro? would the m1's have come from the follicles that were only 11'12's at trigger time?thanks

#4 Geoffrey Sher, MD

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Posted 23 July 2008 - 09:40 AM


An M1 is an egg that has not gone through its final maturational division (Meiosis) where the chromosome pairs split and the  # divides in half (going from 46 to 23). This can be the result of the hCG shot being administered too soon and thus the eggs being "underdeveloped" or "immature"... but it can just as easily happen if the egg is "mal-developed" because it is chromosomally abnormal. An egg can also fail to go from M1-M2 because of the hCG trigger having been given too late resulting in it being “overdeveloped" or "post-mature".

For the above reasons the term "dys-mature" would be a more appropriate term to use than "immature" or  "post-mature".

An egg is an M1 because of underdevelopment prior to the hCG trigger (i.e. truly "immature") has a chance to be maturing to an M2 in the lab. However, if it is an M1 because of "mal-development” or "overdevelopment", it probably cannot be matured in to an M2 through further incubation in the lab and is incompetent (incapable of propagating a "competent" chromosomally normal embryo). Since it is not possible to readily distinguish between "under-developed", "mal-developed” and "overdeveloped" egg under a light microscope, we try to incubate M1 eggs further in the laboratory, in the hope of transforming it in to an M2 but this clearly is not often likely to be successful.

We do not do CGH on M1 oocytes. or embryos derived from them.

Geoff Sher

Edited by Geoffrey Sher, MD, 23 July 2008 - 09:46 AM.