True, it is not unusual or irregular for egg retrieval to yield a few less eggs than the number of follicles would suggest. However, when less than 50% of follicles >15mm fail to yield eggs, something is wrong. So how and why does it happen?
First, a little background information…With the LH surge that precedes spontaneous ovulation and also with the hCG trigger shot given to induce ovulation following the use of fertility drugs, the egg undergoes “ripening” to prepare for fertilization. This involves (among other events) a rapid halving in the number of its chromosomes (meiosis). At the same time, enzymes are released that loosen the cells (cumulus oophorus) that surround and bind the egg to the inner wall of the follicle. This is necessary to enable the egg to come free at ovulation and/or at the time of egg retrieval.
The problem is that with poorly developed eggs, the latter mechanism often fails, leaving such eggs tightly “stuck” to the follicle wall and unable to come free, often in spite of vigorous attempts to flush them loose. That is why the more difficult it is to successfully aspirate an egg at egg retrieval, the more likely it is that such an egg is chromosomally abnormal and “incompetent” (i.e. incapable of developing into a normal pregnancy). This state of affairs is most commonly encountered in women with diminished ovarian reserve (i.e. “poor responders”), women over 40 and in women with polycystic ovarian syndrome (PCOS) who do not receive an optimal protocol of controlled ovarian hyperstimulation (COH).
So the term “Empty Follicle Syndrome” is a misnomer! Yet the circumstances surrounding failure of numerous follicles to yield the eggs they contain at the time of egg retrieval only serves to underscore the need to individualize COH protocols and to time the administration of the “hCG trigger”, precisely.
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