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What’s Going On Back There? Your Embryos in the IVF Lab

Learn what happens to your embryos in the IVF lab during their first week 

Are you curious about what happens with your eggs and embryos in the IVF lab during their first week after your egg retrieval? Well, you’re not alone. Because many of the first days of your embryos occur in the IVF lab, an area off-limits to patients as well as most of our staff, what happens back there isn’t as visible as what goes on in other parts of our clinic. 

Eggs, sperm and embryos also are so tiny that you can’t see them without specialized equipment and microscopes. Your genetic material also requires a pristine environment in which to grow. This includes specialized incubators kept at a constant temperature, special growth media, customized dishes and even an air handling system that filters out anything harmful and keeps the lab at a positive pressure.

The first week is crucial for your eggs and embryos in the IVF lab. These first days see your eggs fertilized and the resulting embryos grow from two cells to about 100. At days 5-7 they reach the blastocyst stage and may be ready to be cryopreserved or transferred. So, since you can’t be there in person watching them grow, here is a day-by-day description of what happens to your embryos in the IVF lab during their first week and the important tasks our embryologists do to help your embryos grow.

Day – 1 Preparation and Lots of Paperwork

What happens to your embryos in the IVF lab?
Dishes being prepared with special medium to help your embryos grow.

The day before your egg retrieval is an important day. What happens with your eggs and embryos during the first week in the IVF lab is well planned out. Before your retrieval even happens, our embryologists begin all of the prep work for your egg and embryo’s first home.

Security and proper identification are of the utmost importance in our IVF lab. Your patient information and demographics along with your cycle plan are carefully entered into our Matcher system, our high-tech barcode system used to accurately match your eggs and embryos to you. Barcode labels and patient wristbands are prepared, paperwork is completed, and all paperwork is labeled through Matcher.

Our embryologists will also be preparing all the dishes your eggs will be placed in as they are retrieved. These dishes are properly labeled through our Matcher system and prepared with a special liquid medium that your eggs will thrive in. Then these dishes go into the incubator overnight to equilibrate.

Day 0 – It’s Retrieval Day!

Our IVF lab staff gets busy right away to get everything ready for your big day. One of the first things they do is process your partner’s sperm sample so that it is ready for the fertilization step after retrieval. The sperm sample is “washed” and concentrated to help them more efficiently select highly motile and quality sperm for fertilization.

During the egg retrieval procedure, your doctor will aspirate follicular fluid into a tube from each mature egg follicle and send these directly to our nearby IVF lab. There, our embryologists are standing by put this fluid into one of the prepared dishes and locate any eggs under a microscope. At this time, the cumulus cells that surround the egg are trimmed and then the egg is placed in a holding dish. If ICSI fertilization will be used, the eggs are then fully stripped of their cumulus cells and their maturity is assessed.

Oocytes, or eggs, that are mature will be fertilized on the same day as your retrieval, typically 4 to 6 hours after. Our embryologists will use the washed and concentrated sperm sample to select a single sperm to inject directly into each mature egg using intracytoplasmic sperm injection, ICSI. Each dish is placed into the incubator which is kept at a constant body temperature of 98 degrees Fahrenheit. And then, we wait.

Day 1 – Fertilization Check

What happens to your embryos in the IVF lab?
Fertilized eggs showing two pronuclei.

Our embryologists checks each dish about 18 hours post ICSI to see if normal fertilization occurred. Under a microscope, they will look to see if the egg, scientifically called an oocyte, shows signs of normal fertilization, specifically if two pronuclei are visible indicating that the DNA from the egg and sperm united. Normally fertilized oocytes will then be moved into cleavage dishes and placed back into the incubator. After the fertilization check, you will get a call from the embryology lab to let you know the number of mature eggs you had and how many appear to have fertilized normally.

Day 2 – Rest Now, Little Em-Babies

We do not look at your embryos in the IVF lab on Day 2, letting them rest and grow in one of our warm incubators. Instead, we prepare all the culture dishes we will need for them on Day 3. These dishes are equilibrated in an incubator overnight.

Day 3 – Initial Assessment and Assisted Hatching Day

On Day 3, our embryologists will look at your embryos under a microscope to assess how well they are dividing and give them a visual grade. Ideally, your embryos should be at 6 to 8 cells with little to no fragmentation and the cells should look symmetrical to each other. If your embryos will be tested later using preimplantation genetic testing, PGT-A, the embryologist will also perform assisted hatching. In this procedure, a laser is used to create a small hole in the zona pellucida (the embryo’s outer shell) to help the embryo expand. Your embryos are then moved to a different dish with prepared blastocyst culture media and placed back into their incubator home.

Day 4 – Do Not Disturb!

What happens to your embryos in the IVF lab?
Your embryos grow in specialized incubators.

This is another day of rest for your embryos in the IVF lab. We do not check them on this day but allow them to continue growing and dividing inside their warm incubator. If you will be having a fresh embryo transfer, our embryologists will prepare any dishes on this day that will be needed for the procedure.

Day 5 – Blast Check and Biopsy

Day 5 is a critical day in the growth of your embryos in the IVF lab. Our embryologists will assess under a microscope if your embryos have reached the blastocyst stage and appear to be growing. At this stage, your embryo will have about 80 to 100 cells and ideally will look symmetrical with little fragmentation. They may also be starting to hatch or completely hatched from their trophectoderm shell. At this stage, depending on your cycle plan, our embryologist may either 1) biopsy the embryo for PGT-A testing, 2) cryopreserve the embryo to use at a later time, or 3) begin preparations for a fresh embryo transfer.

The majority of our patients opt to do a biopsy for PGT-A genetic testing. To do this, our embryologists will prepare a biopsy kit for each patient with barcode labels using our Matcher system for accurate identification of biopsy samples to patient. Each embryo will then be placed in a biopsy dish and a few cells are clipped from the trophectoderm part of the embryo. The trophectoderm is the outer layer of the embryo that will eventually form into the placenta after implantation. After the biopsy, each embryo is cryopreserved using vitrification and stored separately in liquid nitrogen tanks.

The biopsied pieces taken from the embryo, about 4 to 8 cells, are loaded into individual tubes matched to the embryo and patient then cryopreserved using vitrification. After 24 hours, the frozen biopsy can then be shipped in liquid nitrogen to our genetics company where the cells will be tested. 

Day 6 – Repeat

What happens to your embryos in the IVF lab?
A day 5 embryo contains about 100 cells.

This day is generally a repeat of Day 5. Any embryos that were not quite mature enough to biopsy or transfer have been given an extra day to grow. If a patient had many embryos, we may use this day to do the remaining biopsies and vitrification. 

Day 7 – One More Day to Become a Blast

This is the last day that we allow for embryo growth into blastocyst stage. As we have been watching the embryos over the last 7 days, many embryos fail to make it to a blastocyst. This is expected that not all embryos will make it this far. The reason generally has to do with faulty DNA and genetics that occurred at the moment of fertilization when the egg and sperm meet and swap DNA. However, many embryos just need a little more time and by Day 7 may have now matured to a stage where they can be biopsied or transferred. 

On this day, our IVF lab staff will call the patient with the results of how many of their embryos made it to blastocyst and how many were biopsied. If our biopsy samples are ready and have been frozen for at least 24 hours, we will also pack them to ship to our genetics lab.

Whew! It’s been a week!


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