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Egg Embryo Quality

Egg Quality 101

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Why does egg quality plays such a key role in IVF success?

The answer comes down to the simple fact that high-quality eggs produce high-quality embryos, which must then be strong enough to survive the early stages of development in order to result in a successful pregnancy.

With that being said, it's a lot easier said than done, and we realize that the "science" behind of egg and embryo quality may at times be a bit tricky to understand. That's why we've laid out a handful of common FAQ's to ensure you are knowledgeable and confident in the what we do "behind the scenes" in our laboratory.

how important is a lab?

Very. The ability to consistently develop high-quality eggs goes hand in hand with an experienced embryology laboratory and the technologies used. With over 30 years of experience and more than 20 embryologists, scientists and technicians behind the scenes, our  laboratory utilizes innovative technologies and techniques that optimizes fertility success.

what exactly is egg quality?

Egg quality refers to the probability of embryo implantation, based partially on the number of eggs a woman has remaining for the future, or her ovarian reserve. This is related to, but not completely defined by, her age. Likewise, while embryo reserve is a good indicator of egg quality, quantity does not always equal quality. There are women who have a small number of high-quality eggs and who are able, therefore, to achieve pregnancy through IVF.

how do eggs become embryos?

For healthy women, ovulation is signaled each month when the ovaries release a mature egg. The egg travels from the ovary to the fallopian tube, and there it will stay until it is successfully fertilized by a single sperm. After successful fertilization, the sperm and egg grow into an embryo. The process of becoming an embryo is fast: every 12-14 hours the embryo divides.

can you improve embryos?

Our laboratory at Boston IVF uses a unique combination of gases in order to create a consistent culturing environment for all embryos. We are able to create a safe and stable environment for embryo development by monitoring a continual data stream from our incubators, thus creating the conditions for embryos to thrive. Thanks in part to our innovative embryonic incubators, we are able to offer our patients improved embryo quality and fertility success rates.

does egg quality matter?

In a word, absolutely. Eggs and embryos connect with each other in a simple, direct way: high-quality eggs produce high-quality embryos.

High-quality eggs allow the embryo to grow and implant or ‘stick’ once inside the uterus. In order to go on to survive the early stages of development and eventually result in pregnancy, an embryo must be strong (high quality). High-quality eggs and embryos have a higher likelihood of leading to a successful pregnancy. This is the reason age is very important in a woman's chance at a successful pregnancy. As a woman ages, her ability to produce high-quality eggs begins to diminish.

how is egg quality tested?

We know with certainty that age is linked with a decline in ovarian reserve or the number of eggs in your ovaries. Decline in ovarian reserve is connected with a decline in your chances of a viable pregnancy. Age is also tied with egg quality: only twelve percent of all eggs in most thirty-year-old women have the potential to become babies. Only four percent of those eggs remain by age forty. So although egg quality cannot be tested directly, a woman's age is often an excellent predictor/indicator of the quality of her eggs.

What is a day 3 embryo?

A Day 3 embryo references the age of the embryo or the number of days' post-fertilization. The result of a sperm successfully fertilizing an egg is one single cell that begins a rapid process of dividing. After three days of natural dividing, we determine if the embryo, now a Day 3 embryo, has continued dividing properly and is a healthy candidate for implantation. If the embryo is healthy, it is allowed to continue developing naturally for two additional days, so that it can become stronger and more viable for implantation. In cases where an embryo is deemed unlikely to grow stronger, the embryo will then be transferred on Day 3.

what is a day 5 embryo?

As you can probably deduce, a Day 5 embryo is an embryo that has been allowed to develop for five days' post-fertilization. At this point, the embryo contains hundreds of cells and is highly developed, making it well-suited to attach to the uterine wall via implantation. Day 5 embryos are also called blastocysts, and only one-third of all embryos are capable of growing to this stage. Some laboratories are unable to cultivate an embryo to this stage. If your embryo develops to the blastocyst stage, it has a stronger chance of implanting because it is a superior, healthy embryo.

how do WE choose?

In order to decide which embryos to transfer, close observation of all embryos is key. At Boston IVF, our doctors, scientists, and laboratory embryologists closely observe embryo development in the lab, and communicate with each other in order to best determine which embryo to select for transfer.

Your fertility team knows that all groups of embryos are unique. Sometimes the best embryo is immediately apparent; at other times it takes a few days to see which is best suited for transfer.

what is the embryo grading process?

"Day 1" is when after the sperm has entered the egg and we see two circular pools inside the one large round cell. When these two pools are present, we know that the egg has been fertilized by the sperm.

Grading of embryos until the 3rd day is based on three main points:

  • Counting how many cells the embryo has
  • Matching the number of cells to the day of development: for example on day 2 it should have 4 cells and on day 3 it should have 6 to 8-cells
  • The final marker of a good embryo is that the cells should not be breaking apart. 

Grading of embryos on the 5th and 6th day:

  • The embryo starts to look like a ball with a sack of fluid inside it
  • The larger and more expanded the fluid the better
  • The embryo has a button of packed cells in one area that will go on to form the baby. The tighter and more numerous these cells are the better.
  • The button of cells are surrounded by flatter cells that form the outside of the ball. These cells go on to form the placenta. 
  • At this stage you can’t count the number of cells, as an embryo should have more than 50 and sometimes over hundred cells

i had an unsuccessful cycle. should i keep trying?

Although age is a key factor in egg quality, embryo quality, and pregnancy rate - there are variations from month to month. This means that even if your first cycle was unsuccessful, you have reason to maintain a sense of hope. Definitely try again.

what tests do you offer?

At Boston IVF, our embryologists, doctors, and scientific team continue to improve your success rates through the use of the following tests:

+ PGT-M: This genetic testing method is performed on an IVF embryo prior to transfer to your uterus. PGT-M reveals any present single gene disorders. Through PGT-M, we can establish whether you and your partner are at risk of having a baby with a specific genetic disease and eliminate the chance of passing it on to your children.

+ Preimplantation Genetic Screening (PGS): Rather than reveal single gene disorders, PGT-A tests for chromosomal abnormalities that could result in birth defects or cognitive impairment. Performing this test increases pregnancy rates and leads to the birth of healthier babies. Doctors and embryologists are able to select only healthy, chromosomally-normal embryos to implant

+ Assisted Hatching: When embryos have lower metabolic activity, they may be unable to escape from their ‘shell’ to implant into the uterus. In these cases, our doctors can facilitate the hatching process by using a tiny pipette with acidic solution to make a miniscule opening that allows the embryo to then implant.


We look forward to speaking with you, and will be in touch as soon as possible!