Today we live in a world where PGS-testing has become a major tool we use to pick which, if any, embryos get transferred. Embryos with normal PGS results are the first to be transferred. In theory, one would imagine that if you started with the same set of eggs, and the same set of sperm, euploidy or aneuploidy would be predetermined: those eggs and sperm either had the normal or abnormal number of chromosomes to start with, and nothing could change that. Well, we now have a fair amount of evidence that this logical theory isn’t reality: this month has brought more data showing that some clinics may have the ability to influence whether your embryos are more, or less, likely to be euploid and fit for transfer.
Why This Study Is Special
First, the sample size of embryos is large at nearly 14,000 and came from a wide variety of centers (over 40), so we’re working with a lot of data that should reflect what happens in the real world. Second, the nature of these embryos and the women who produced them was likely homogenous: young, healthy egg donors who typically meet the same criteria clinic-to-clinic. So we’re silencing the variability between who typically shows up at two different clinics. Third, a single reference laboratory did the PGS testing, counted the chromosomes and determined whether the embryos were good or not.
What Was Tracked & What They Found:
The authors found meaningful variability between clinics and determined at least 25% were above or below the average in a statistically-significant way. How dramatic were the outlier’s results? The average clinic recorded 67% of embryos were euploid, but clinics on the higher end saw rates into the 80s and on the lower end rates into the 30s.
So if this is real, what could be going on here? Two major guesses. First, some clinics prescribe different or higher doses of gonadotropins and there is some pretty interesting data that the more gonadotropins a patient takes, the lower the proportion (but not absolute number) of euploid embryos she will produce. Second, it’s possible there is a difference in how the labs at these clinics grow their embryos that leads to chromosomal abnormalities (or helps correct them).
The Study’s Limitations
This is a good study (otherwise we wouldn’t bother you with it), but there are some shortcomings. First, it’s retrospective and so it’s harder to randomize patients, ensure they’re similar and control for other possible variables. Second, the platform used here (array CGH) to count chromosomes is not what’s widely in use today (Next Generation Sequencing has gained popularity in the past few years). That said, the investigators were consistent in using this method across all samples and we’ve started to see data the same findings were upheld using Next Generation Sequencing. Finally, chromosomal count is a surrogate marker, and a valuable one, but as patients we care more about real-world endpoints (Did I get pregnant? Did I deliver? Was my baby healthy?).
The Takeaway
This should reinforce your conviction that where you are treated very much matters. Even for healthy, good-prognosis patients, let alone for those of us with more complex histories. Understanding variables like which protocols you are likely to be put on (and the rationale), as well as the quality of the laboratory, are important factors to push your clinic on before making a decision.