We think of the laboratory as a mill because it’s work flow is linear: it must fertilize eggs, cultivate embryos, be able to biopsy those embryos for genetic testing, and then be able to freeze embryos (or eggs) and thaw them for future use. The continuum, along with rates of mere “competence” and “excellence” look something like this. We’ll cover each in this chapter. It’s worth noting that some laboratories may have lower scores on some of these parameters and for acceptable reasons (e.g. maybe they see particular hard patient types). It’s completely within your right to probe exactly on why this is the case and why they're confident this reasoning explains most of the underperformance.
Laboratories must inseminate the retrieved eggs with sperm and this is done by one of two processes:
Both techniques require sophistication and practice. According to the panel of surveyed embryologists a “passable” laboratory should be able to fertilize a minimum of 60% of retrieved eggs using CI and 65% of mature eggs using ICSI. We believe those numbers are low and the floor for acceptability should be 70%. A “benchmark” laboratory should have fertilization rates into the high-70s, or low-80s, for either procedure. When performing ICSI, “benchmark” laboratories should damage less than 10% of the mature eggs available.
Once the eggs have been fertilized, laboratories have the daunting task of trying to grow embryos to a stable state. This is a difficult process and many laboratories are only able to keep embryos alive for 3 days, up until a point when the embryo has 8 cells and enters “cleavage stage.” This is still a very fragile period for embryos.
More sophisticated laboratories can grow embryos to “blastocyst stage,” when the embryo has hundreds of cells and is more developed and stable. The earlier an embryo reaches blastocyst stage (often on Day 5), the quicker it grows and the healthier it is. In many laboratories, blastocyst embryos are more likely to lead to a live birth than cleavage stage embryos.
Should you want to genetically test your embryos, your clinic’s laboratory will need to cleave a few cells from the embryo and send them to an outside “reference laboratory” for testing. When embryologists take too few cells from the embryo, no reading can be made. When the embryologist takes too many cells, as one laboratory has recorded (see below), live birth rates can be impaired.
For this reason, if you think you want, or need, to have your embryos genetically tested, you should go to a clinic that is skilled at biopsy. There is no perfect measure for excellence here but a good measure is the “Successful Biopsy Rate,” or the proportion of embryos that were biopsied so that enough DNA was detected in the sample for a good reading. “passable” labs should have 90% success rates and exceptional labs should have 95% rates. Unfortunately this measure does not account for how often an embryologist takes too large a sample, which is problematic.