Ask an Expert: Embryologist Part Four

Ask an Expert addresses reader questions every week. Today we share expert insight from Kristen, an Embryologist who will answer all of the remaining questions related to fertilization, egg and sperm, frozen cycles, and safety precautions.
Embryo Fertilization
Why do so many embryos stop growing after day 3 and not make it to day 5?
The egg has everything in it that it needs to grow to day 3. After day 3, the genome of the embryo has to activate and this is a common point of issue. It may be egg or sperm related. It is also a time of massive structural change as the embryo needs to progress from individual cells of 6-12 cells to a blastocyst containing hundreds of cells. The cells of day 3 or 4 embryo need to compact together and then perform cavitation (make a big hole or cavity) and blastuation (form the inner cell mass and trophectoderm).
What are some causes of a high number of eggs retrieved but low fertilization rate?
The egg has not allowing the sperm in, or the sperm are unable to activate and get in. Some eggs have an issue where it is unable to perform its final task of exuding half of its chromosomes into a polar body, so it never makes a mature egg. Cases of higher egg numbers usually do have higher number of immature eggs, but not always. Sometimes, we are just unable to know why. A lot of patients with poor fertilization with IVF can have fantastic results with ICSI in a subsequent cycle.
Egg Q&A
Have you seen an egg collection where all eggs were immature?
Yes, it’s rare but does happen
What can you tell about egg quality just by looking at it?
At the egg collection the eggs are surrounded by the cumulus-oocyte complex but sometimes we can see that the egg is small and dark and likely immature. It’s not until the ICSI, or fertilization check for those not having ICSI, that we can see if the egg is mature or small, pitted, granular, vacuolated etc.
Does high mature rates and fertilization signify good egg quality?
Not necessarily. Good embryos and pregnancy rates do. You can get lots of mature eggs and good fertilization and very poor embryo development which is largely from poor egg quality
Sperm Q&A
What is the best method to isolate mobile sperm with ICSI with low sperm count?
Different labs have different methods that they use to isolate sperm. One such method is using a hyaluronin dish or media containing hyaluroning such as Sperm Slow. Mature sperm have many hyaluronin receptors and will bind to the media or get trapped to the dish. These sperm are selected for ICSI.
How much does sperm DNA fragmentation affect the quality of embryos?
Quite a bit as embryo quality tends to be much poorer. If a male has known high DNA fragmentation then ICSI can be performed as a way of reducing this, as there are sperm selection techniques that allow for sperm to be chosen that have better quality DNA. The egg has a mechanism, which can repair DNA damage from the sperm, but the sperm has no such mechanism and the egg can only repair so much. As women (and their eggs) age, the repair mechanism capabilities reduce.
How much do you rely on morphology if also doing PGS?
The genetic result will beat the morphology for selection. If multiple embryos test normal then morphology will be used too.
General Q&A
What is the likelihood of embryos not surviving the thaw? Why would an embryo not survive a thaw?
About 5-10% don’t survive. Embryos can get affected by the freezing and thawing process as a lot of expanding and contracting occurs with the introduction of cryomedia and thawing solutions.
What processes are in place to ensure your embryos are indeed your embryos?
Labs have verification and witnessing protocols in place and some labs employ automated or barcode witnessing systems. At each step of the way, each item is verified. For example, at egg collection when the eggs get put into the patient’s dish, when sperm gets added, when embryos get transferred into a new dish, when embryo goes into transfer catheter or freezing dish, that dish is double verified that they match up.
Are frozen transfers more successful than fresh ones?
There has been a school of thought that stimulation from a fresh cycle negatively affects the endometrium and all embryos should be frozen and put back on an unstimulated cycle. However, this appears to only be true for women who get a large number of eggs, like over 15. If a woman is not overstimulated and her endometrium is a good thickness then success rates with a fresh transfer are just as good. Statistically, fresh and frozen transfers have similar success rates.
Aside from grading, how do you choose which embryo to transfer?
If several embryos have a similar grading then we look back and determine which one had the most ideal development along the way.

Kristen has been an Embryologist for 5 and a half years. She studied Biomedical Science and has a Master’s degree in Reproductive Medicine. She’s always had a passion for fertility and a desire to help others going through such a hard and emotional journey.

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