Our Embryologist Answers Your Preimplantation Genetic Testing Questions

TRM’s senior embryologist answers some of the most common questions about a complex procedure and the IVF lab

Most people familiar with Tennessee Reproductive Medicine know Dr. Rink Murray and Dr. Jessica Scotchie, but there are so many talented people who make up TRM. A wonderful group of folks, from the front desk staff to nurses and beyond, fuel TRM’s passion.

TRM’s senior embryologist Shan Wilkinson answers some of the most common questions about a complex procedure and the IVF lab | Tennessee Reproductive Medicine | Chattanooga, TN

We wanted to share more information about the people behind the scenes, specifically TRM’s Senior Embryologist Shan Wilkinson. Shan shared information about some of the most complex procedures in the in vitro fertilization (IVF) lab: preimplantation genetic testing (PGT), which has recently replaced preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) as the preferred medical term for embryo genetic testing. First, a little shop talk with our senior embryologist.

What does a typical day in the lab look like?

When we are “in cycle” (during egg retrieval/embryo transfer/biopsy weeks) we start the day by testing the incubators. We check to ensure each occupied incubator is maintaining the proper temperature and gas environment. All other heated surfaces such as tube warmers, hot plates and microscope stages, are tested for proper temperature each morning as well.

Egg retrievals, fertilization checks, embryo thaws and embryo morphology checks are performed in the mornings. Embryo transfers and embryo freezing are performed late morning and early afternoon. Five to six hours after retrievals, we perform intracytoplasmic sperm injection (ICSI).

When we are not “in cycle” (down time between retrieval/transfer/biopsy weeks) we perform any necessary maintenance. Empty incubators are put through a “contracon” cycle where they reach 90°C for an extended period of time to burn off any potential contaminants or volatile organic compounds. All laboratory surfaces, like the cabinets, countertops, floors and equipment, are wiped down to remove any dust or debris that may have been introduced during the busy IVF cycle.

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In any given day there is also data entry, record keeping and patient communication that occurs. The embryologists and lab staff are also always preparing for the next day, week, month.

What’s the difference in PGD, PGS & the new PGT (preimplantation genetic testing)?

Let’s start with the older terms people are familiar with. Embryos from patients who are known carriers of a specific disease state or have what is called a chromosomal translocation are tested through PGD, or preimplantation genetic diagnosis. Patients who undergo PGD are trying to avoid having an “affected” child or, in the case of balanced translocations, trying to avoid repeat miscarriage.

PGS is preimplantation genetic screening and analyzes all 23 sets of chromosomes. PGS is indicated for use in patients with advanced reproductive age, repeat pregnancy loss or those who desire “family balancing,” which is selecting an embryo for implantation based on its sex, allowing for a boy or a girl. You may also hear of this type of screening referred to as comprehensive chromosome screening or CCS.

Related Reading: Your Baby, Your Right to Sex Selection. But Is it Wrong?

That being said, the global reproductive community including embryologists is moving away from PGD/PGS and simply referring to all testing as PGT (preimplantation genetic testing). The addition of a qualifier to PGT identifies the reason the testing is being sought or the type of testing required. PGD is now either PGT-M (monoclonic/single gene disorders; sickle cell for example) or PGT-SR (structural arrangement of chromosomes) and PGS is referred to as PGT-A (aneuploidy).

What are the benefits of PGT?

In theory, PGT should decrease miscarriage rates and increase the chances of having a healthy baby. It is also a useful selection tool when dealing with a large cohort or group of morphologically equal embryos and allows us to transfer a single genetically normal embryo rather than one or two embryos with unknown chromosomal integrity.

What should patients understand about the process?

  1. In our laboratory, about 50% of fertilized embryos develop into embryos suitable for biopsy by day 5, 6 or 7. Some embryos will grow to the blastocyst stage by those days. However, if they don’t have a healthy number of cells, they will not survive the biopsy/freeze/thaw procedure. We try not to freeze anything that would not have the potential to become a baby after thaw and transfer. We also know the sex as part of the testing and want the patient to decide if, and when, they want that information released.
  2. PGT is a useful tool in determining the best embryo to transfer, but it does not guarantee a pregnancy.
  3. A wider range of patients is using PGT more frequently. It is a helpful tool and is becoming increasingly accurate, but not perfect.

What is the best part of the day for an embryologist?

The best part of our day is when we get to be the bearer of good news! This is especially true in regard to genetically tested embryos. Pregnancy test results are usually relayed by the nurses and doctors, although embryologists and lab staff excitedly watch for lab results to be reported.