The IVF Laboratory

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:

• Conventional Insemination (CI) occurs when the egg is surrounded by droplets of sperm and left overnight to fertilize.
  
  
• Intracytoplasmic Sperm Injection (ICSI) occurs when the embryologist selects a single sperm and injects directly into the egg.

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.

We recommend only going to a clinic with a laboratory capable of growing embryos to “blastocyst stage.” If a laboratory insists upon doing Day 3 transfers, “passable” labs should be able to grow on average (across its patient base) 45% of fertilized eggs to Day 3, whereas the exceptional “benchmark” labs should be able to grow 70% of fertilized eggs to this stage. We should note these are averages and they do not necessarily mean or reflect that the clinic could do this for all patients or you specifically. Along those same lines, if your laboratory aims to do a Day 5 or Day 6 transfer, “passable” labs should be able to grow 40% of fertilized eggs to Day 5 or Day 6, and exceptional labs should be able to grow 60%.

We should note that some laboratory directors think a better benchmark is the “usable blastocyst conversion rate” which is slightly more demanding & quantifies the percentage of fertilized eggs that grow into embryos that get either transferred or frozen. Even still, the same benchmarks (40% = passable, 60% = excellent) apply for “usable blastocyst conversion rate”.

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 95% success rates and exceptional labs should have 98% rates. Unfortunately this measure does not account for how often an embryologist takes too large a sample, which is problematic.