Fertilization & Culturing

During this phase, the clinic’s science team will bring together the eggs and sperm to create and develop the best embryos possible.

Making Your Decision

Prior to your egg retrieval, you will discuss your treatment plan with your provider. Together, you will determine how many eggs will be fertilized and which fertilization approach will be used. Eggs can be frozen without fertilization, but are more fragile to the freeze and thaw process than embryos.

Fertilizing the Egg

Once the egg is retrieved (or thawed, if frozen) and the sperm sample is prepared, it’s time for fertilization. In most cases, we perform Intracytoplasmic sperm Injection (ICSI). ICSI is a technique to inject a single sperm into each egg.

This yields higher fertilization rates and lower abnormal embryo rates and can even be performed with poor quality sperm. For those that prefer it, traditional fertilization can be performed as well by placing the egg and sperm together in a special dish.

Fertilization Tips

The markers (pronuclei) we use to determine fertilization can disappear, which is why some Day 1 embryos are “unconfirmed”; we won’t be able to tell if they are fertilized until our Day 3 check

Sperm are selected based on morphology (physical condition) as well as motility (swimming ability) individually by embryologists before ICSI

Some abnormally fertilized embryos can form normal blastocysts and should be cultured to Day 5 and PGT tested; Day 3 cryo not recommended

ICSI is the process of injecting individual sperm directly into the egg using a specialized glass needle on an inverted microscope
to achieve fertilization

If immature eggs (GV/MI) do not mature to MII by Day 1, they are discarded as their quality will be far too low to feasibly produce results. (another lab dont mature eggs)

Egg and Embryo Development

Five days after the Embryo Transfer will be your first progesterone check, and four days thereafter will be your first pregnancy check followed by another confirmation one just a couple days later. With luck that moves you into the final step of the process:

OB Monitoring & Graduation

Culturing the Embryo

The embryologist then carefully let your embryos develop in incubators, typically until 5-7 days after fertilization though some may be cultured till day 3. During this time, the embryologists closely monitor the embryos for signs of healthy growth and development.

Though not all embryos will reach this stage, at the end of this process, we will share quality grades for the embryos and be able to identify the embryos ready for biopsy.

Notes on Culturing and
Embryo Quality

  • Embryo grades are on a spectrum. Embryos with the same grade are not necessarily the same quality of embryo.
  • Day 3 grades are not a completely reliable indicator of future development
  • A compacting embryo on Day 3 has started the process of becoming a blastocyst and is an indicator of good quality
  • Most embryos arrest (stop growing) on Day 3 as the transition from Day 3 to 4 is a difficult developmental checkpoint.
  • An arrested embryo will never restart development.
  • Freezing an embryo on Day 3 will not save it from arresting at a later date if that is the embryo’s destiny.
  • We determine if an embryo is arrested based on developmental progress. Even if development is slow, if it has progressed from the previous day it is not arrested.
  • Arresting of embryos at or before this stage is more attributed to egg quality.
  • Very slowly developing embryos should not be frozen on Day 3 as their chance of arresting is too high to recommend transferring.