Mature eggs

[nuthinbutpink]

After ER, the doctor is able to tell us how many eggs they were able to get and sometime later you hear how many were "mature" and then we get the fert report.

Sometimes there is a large discrepancy as to number of eggs retrieved and the number that are mature and a subset of those fertilize. What makes an egg "mature"? Is it just size? How can you tell a bad egg from good one and how soon after a retrieval is this known usually?

[Carole]

That's a good question. The embryologist's first look at the egg is obscured by a cloud of cumulus cells called the oocyte cumulus complex that surrounded the egg inside the ovarian follicle and both egg and cumulus cells are sucked out with the egg during the egg retrieval. These cells make it hard for the embryologist to see a structure called a polar body which is produced by the egg when it is mature. This polar body is a cell membrane enclosed sac of excess chromosomes that the egg must remove before it can successfully combine with the sperm DNA during fertilization. So, how and when does the embryologist know the egg is mature? Immediately at retrieval, the most the embryologist knows is the number of oocyte-cumulus complexes retrieved. Occasionaly, clouds of cumulus cells are recovered at retrieval that don't contain an egg. That is why the doc and patient may get a report of 20 eggs retrieved and later the report is revised to less than that. If the eggs are to be injected, then the cumulus cloud is removed from the egg by the embryologist to allow visual verification of the polar body and hence maturity of the egg. You will get a reliable count of mature eggs at the time of cumulus removal for ICSI- sometimes cumulus removal is called "stripping" the egg. Only eggs with a polar body (=mature eggs) can be injected. Eggs do mature naturally in vitro if they are real close to maturity at the time of retrieval, so sometimes you might gain a mature egg the next day and have a late egg injected at that point, again causing a change in the number of mature eggs. Regarding size and maturity, size is usually not a distinguishing factor. It is true that over the months it takes an egg to mature in your body, it expands dramatically in size but by the time of retrieval, eggs that are retrievable are usually very similar in size. Sometime extra large eggs double the size of the others are recovered but these jumbo eggs invariably are chromosomally abnormal, usually containing multiple extra sets of chromosomes. "Bad eggs" at retrieval are usually very dark in color, and may appear shrunken or actually broken, with or without leaking cytoplasm. The number of eggs that fertilize is very frequently less than those that are initially retrieved for all the reasons above. The reduction in egg number at each step is due to the fact that not all cumulus complexes retrieved contain eggs, not all retrieved eggs are healthy or mature, and even some mature eggs may not fertilize. You can see pictures of normal cumulus eggs and later stages of embryo development at this previous Fertility Lab Insider post:
http://fertilitylabinsider.com/2010/11/embryo-stages-progression/
Hope this helps. :)
Carole

[nuthinbutpink]

Awesome information! Thank you so much!

[grits]

Thank you for this information!

[JackiesHope]

Thank you!

[TWINSplz!]

Thanks for the info!

[grasshopper]

Wow...interesting stuff. Just curious as to what do you feel most often causes "bad eggs"...over/understim/protocol or the woman's own egg quality issues? Does a "bad egg" ever surprise you and turn out ok?

[Carole]

Grasshopper,
Honestly, we almost never really know why an egg is "bad", meaning broken, unable to be fertilized, shrunken etc. You are correct that it can be due to overmaturation by stimming too long. Sometimes a lead follicle is "sacrificed", if a longer stim will allow a large following cohort of eggs to mature together. Sometimes eggs are cracked because they are inherently fragile due to some zona defect but this is rare. If cracking occurs in more than an occasional egg, it can mean that the pump pressure on the retrieval pump is set too high and the resulting shear forces crack the eggs. Eggs from some women (for example, older women) may not fertilize or fertilized eggs may not divide, even though they looked normal- bright, clear, no cracked zona etc. Non fertilization/developmental problems may be due to aneuploidy, a genetic condition inside the egg that is not visible. If the egg is very dark, shrunken or leaking cytoplasm, I have never seen it turn out okay because these are all signs of cell death. Hope this helps. Carole :)

[grasshopper]

It does...thankyou. I've always loved hearing about things on a cellular level...never fails to spin me out.

[Dreaming]

Thank you for this very interesting information. Can I ask you a question about my last cycle? I had 13 eggs retrieved (from follicles sized 18-23mm) yet only 2 of my eggs were mature. My RE was very surprised that so few were mature and said this was quite rare. What do you think happened and is there anyway for such eggs to be matured in the lab? I don't think I had a quality issue as I was very lucky to become pregnant with 1 of those 2 eggs but I always wonder why I had so many immature eggs. Thanks!

[Carole]

First, congratulations on your pregnancy. That's terrific. It is unusual to have so few eggs from large follicles but certainly not impossible. Sometimes eggs that are very close to mature will spontaneously mature in the lab. For eggs a little less mature, it is possible to coax them along in maturation medium but not all programs offer this. There is a downside to maturation in vitro which is that we don't really understand exactly how to mimic the natural maturation process in vitro though this area is an intense research area. The ovary is so marvelously complex and fine tuned- it's hard to duplicate in a culture dish. So the eggs matured in vitro produce a polar body- a sign that they are mature on one level but maybe not fully matured in other areas- for example- maternal imprinting. There is some evidence that long periods of in vitro maturation may cause large offspring syndrome. I wrote about that in my blog if you want to read more about it. So the answer is I don't know why you had so many immature but in the end, as you say, it didn't matter because you are pregnant now. Best Wishes, Carole :)