My family has always supported me through my journey towards becoming a scientist.  This is why when they have questions that are science related, I’m always happy to return the favor and support them by sharing the knowledge I’ve gained. Knowing that I work for a fertility company, my cousin who is considering PGS testing recently contacted me to find out some of my thoughts.

First, I gave her the basics: PGS, or preimplantation genetic screening, is a genetic test performed on IVF embryos with the goal of helping improve the chance of a successful cycle. This is done by analyzing the number of chromosomes within each embryo. Embryos with the correct number of chromosomes are more likely to lead to a successful cycle; whereas embryos with extra or missing chromosomes typically fail to implant, lead to a miscarriage, or result in the birth of a child with a genetic condition. By transferring an embryo with the correct number of chromosomes, you have a higher likelihood of achieving an ongoing, healthy pregnancy. That’s the gist, but since I’m a scientist, I wanted to dive a little deeper into what happens in the laboratory to make PGS possible. Below you’ll find a behind the scenes look at what goes on in your IVF lab in order to prepare your embryo for PGS. Not all IVF labs are the same, so I’ve also put together some questions you can take to your IVF center to learn more about their lab and their processes.

Cells are Removed from Embryos through a Biopsy

In order to assess the chromosomes within IVF embryos, some cells must be removed from the embryos through a procedure called an embryo biopsy. When people find this out, often their initial thought is “Wouldn’t that hurt the embryo?”

To answer that question, I find it’s helpful to know a little bit more about how an embryo is biopsied. About five days after fertilization, if all goes well, embryos will reach the stage of development known as the blastocyst stage. As blastocysts, embryos contain approximately 100 to 200 cells, divided into an inner cell mass and an outer ring of cells called the trophectoderm. The inner cell mass is a grouping of undifferentiated stem cells that will go on to eventually form the fetus. The trophectoderm is a layer of cells that will become the placenta and other supporting structures of a pregnancy.

During the IVF process, the embryo is floating in a special liquid (known as media) that provides nutrients to aid in proper growth and development. Keep in mind when the embryo is biopsied, it is roughly the size of a grain of table salt, so removing a few cells from something so tiny is no trivial matter. Under a microscope, a skilled embryologist can use special tools to hold the floating embryo still and gently remove 5-10 cells from the trophectoderm which can be sent to the genetic testing laboratory. 

After reading a lot of studies on IVF procedures, I think it’s important to point out that new techniques have been developed and implemented over the past decade that have made biopsy a lot safer for the embryo than it once was, especially when performed by a well-trained embryologist. Like any medical procedure though, there are still risks involved and it’s a good idea to go over these with your doctor.  

Questions to ask:

  • Does your clinic routinely perform embryo biopsies for PGS?
  • What is your clinic’s biopsy success rate?
  • How old is the laboratory equipment being used? Does the lab have the latest and most advanced tools available?

Embryos are Frozen while Awaiting Transfer

After biopsy, the embryo is typically frozen while PGS testing is performed. New techniques in assisted reproductive technology include methods for freezing the embryo- one such technique “flash-freezes” the embryo to prevent damaging ice crystals from forming. This is called vitrification, and it typically results in high rates of embryo recovery.  Some studies have suggested that certain patients have increased ongoing pregnancy rates when embryos are frozen before transfer (Wu et al., 2018). It is thought that by freezing embryos before transplantation, you can avoid certain risks, and in some cases, potentially even contribute to a better environment for embryo transfer and implantation (Bhattacharya, 2016; Simopoulou et al., 2014). The benefits of freezing embryos and waiting to transfer can vary depending on the specific circumstances of the patient.

Questions to ask:

  • Considering my age, number of eggs retrieved, embryo quality, number of embryos available, history etc., which is the better option- fresh or frozen embryo transfer?
  • In terms of successful pregnancies, how does frozen vs. fresh transfer compare at this clinic?

Handling Embryos Requires Great Skill and Precision

As previously mentioned, physically handling the embryo requires special training. Many clinics have their own training systems and typically senior embryologists with more experience will perform the embryo biopsies and vitrification procedures. There are also special hands-on training programs that teach embryologists the latest techniques for fertilization, caring for the embryo in vitro, handling the embryo, performing biopsies, and freezing the embryo.

Questions to ask:

  • Does your clinic routinely perform embryo biopsies for PGS testing?
  • How are your embryologists trained? Are senior embryologists working on my embryos?
  • What are the statistics for successful pregnancies at this clinic broken down by factors like maternal age, frozen or fresh embryo transfer, whether or not PGS testing was done and so forth?

You’re head may be spinning after all of that! As I mentioned at the beginning, I love talking science, but when you’re going through IVF and considering whether or not to do PGS testing, this isn’t just science; this is a test that can seem complex and intimidating. It is my hope that in explaining to you the process, helping you understand the basics and offering you questions you can ask your doctor, it can give you the confidence to make the decision right for you. Ultimately, I want to give you or any patient that seeks my advice the same support my own family has given me in my journey to become a scientist in the first place. That way, I can return the favor and give you the advice I’d give my own family to help you build yours!


Bhattacharya, S. (2016). Maternal and perinatal outcomes after fresh versus frozen embryo transfer—what is the risk-benefit ratio? Fertility and Sterility, 106 (2), 241–243.

Simopoulou, M., Asimakopoulos, B., Bakas, P., Boyadjiev, N., Tzanakaki, D., & Creatsas, G. (2014). Oocyte and embryo vitrification in the IVF laboratory: a comprehensive review. Folia Medica, 56(3), 161–169.

Wu, M.-Y., Chung, C.-H., Pan, S.-P., Jou, G.-C., Chen, M.-J., Chang, C.-H., … Yang, Y.-S. (2018). Advantages of cumulative pregnancy outcomes in freeze-all strategy in high responders – A case-control matching analysis of a large cohort. Journal of the Formosan Medical Association = Taiwan Yi Zhi.

Malania Gaddis

Malaina Gaddis is a Genome Variant Scientist at CooperGenomics where she analyzes DNA mutations identified through carrier screening to determine whether or not they contribute to disease. Malaina received her B.S. in Biology from Brigham Young University, her PhD in Genetics, Molecular and Cellular Biology from the University of Southern California, and her M.S. in Bioscience Management from the Keck Graduate Institute. She is particularly excited about using genomics and genetic testing to help patients receive personalized care.