This month’s blog is a Q&A of the top five questions our Utah Fertility Center team commonly gets about embryology. This branch of biology and medicine is concerned with the study of embryos and their development. Embryologists are scientists who combine the sperm and egg to help an embryo grow in a controlled environment, and because of this, they play a central role in your IVF journey!
Q1 – How are embryos graded?
The day after your egg retrieval, you will get your fertilization report. During the next few days, any fragmentation will be noted, which happens when there is uneven cell division (where parts of the cell break off). Not to worry, fragmentation is fine as long as you have a good cell number and cell symmetry.
After day 3 the embryonic DNA takes over, including the genetic contribution from the sperm. When grading a blastocyst, the embryologist is looking at the degree of expansion, the inner cell mass, and the trophectoderm (cells surrounding the outside of the blastocyst). The best grade embryo shows large expansion, plenty of uniformly-sized cells in the trophectoderm, and an ICM (inner cell mass – a small cluster of cells on the inside of the blastocyst which develops into the fetus) along with lots of tightly packed cells.
Every embryo is given 2 letter grades along with a description of the level of expansion (A, B, or C). The first letter grade corresponds to the ICM and the second to the trophectoderm. This means if the embryo got an “AB.” grade, that means a great ICM with a grade A, and a good trophectoderm with a grade B.
A grade of “BC” simply means the trophectoderm looks lower quality, but can still work. You don’t need an AA embryo to become pregnant. In fact, most of the embryos we see that result in a baby come from grade BB and BC embryos! The grade only indicates the potential to implant.
Source link: https://www.utahfertility.com/understanding-embryo-grading/
Q2 – What are the most common causes for embryos to arrest?
In the first couple of days of conception, the sperm and primarily the egg health determine fertilization and initial cell division. On day 3 the genome (first cell of human life) takes over which contains the embryo’s complete set of DNA. Embryos that cease development after this point are often due to genetic issues of the embryo. Other possible causes of embryo arrest is DNA fragmentation, mitochondrial defects or stressors in the lab (humidity, temperature and ph).
Q3 – Do PGT-A-tested embryos have higher success rates?
Any time an embryo is conceived, whether in a spontaneous pregnancy or as part of an IVF cycle, there is a risk the embryo will have an incorrect number of chromosomes. Too few chromosomes is referred to as monosomy, too many chromosomes is referred to as trisomy, or missing or extra pieces of chromosomes referred to as partial monosomy/trisomy.
Most chromosome problems are not inherited; they occur by chance alone. As a woman ages, the risk to conceive an embryo with a chromosome problem increases. But all embryos have a baseline risk of having an incorrect number of chromosomes, regardless of the age of the mother or egg donor.
Preimplantation genetic testing for aneuploidy, or PGT-A evaluates the embryos and the apparent number of chromosomes is determined. A small sample of cells are taken from each embryo through a biopsy and sent to a special laboratory for testing. Euploid embryos have the correct number of chromosomes. Aneuploid embryos have an incorrect number of chromosomes and mosaic embryos show some cells with the correct number and some with an incorrect chromosome number. Together with your doctor you can work to prioritize those embryos that are genetically normal for transfer. This information alone can increase success rates and lower the chance of miscarriage. PGT-A is most useful for women in their late 30’s and early 40’s as the percentage of aneuploid embryos increases with age.
Q4 – How long can embryos remain frozen?
Indefinitely. Through a process called cryopreservation, embryos are frozen and stored in liquid nitrogen at minus 320 degrees Fahrenheit (minus 196 degrees Celsius), a temperature that stops all biological activity. Since all biological activity has ceased, then you essentially hit the pause button and things should resume when you take the pause button off.
Q5 – Can you tell if my embryo is a boy or a girl?
Not by viewing through a microscope. The only way to tell the gender of an embryo is through genetic testing.
We hope these answers help you better understand the role of embryology in your IVF journey. Our experienced fertility teams at our various Utah Fertility Center locations are here to help make your fertility journey as comfortable and smooth as possible. Our caring endocrinologists and embryologists all have one goal, to help you achieve your goal of conceiving!