Egg and Embryo Development

Sperm, eggs and embryos are handled in the Embryology Lab, where they are identified, processed, and evaluated in a special environment. After Egg Retrieval, the egg will be identified, then placed into an incubator for 4 hours before fertilization. On the Retrieval day, embryologists will inform you of the number of retrieved eggs and discuss your embryo culture plan.

Day of the
Egg retrieval

After the physician retrieves the eggs, they are passed to the embryologist who will examine them under a microscope to determine the number retrieved. We’ll be able to determine their maturation 4-6 hours after retrieval.

Egg Maturation Stages

*You will see these indications of maturation development in your embryo update on Day 1 of your embryo development. If your egg is mature, our embryologist will fertilize them with ICSI (Intracytoplasmic Sperm Injection) or by conventional fertilization per patient’s request.

Day 1 of Embryo Development

On Day 1, you will receive an email update with the progress of your eggs, including whether your eggs were fertilized. If they were, their culture plan will often be to continue culturing until Day 5 to see if they will develop into blastocysts. If your egg remains at an immature state (MI or GV), this means that the egg is unable to mature and will be discarded.

If your egg retrieval was on a Saturday, your Day 1 update will be postponed and sent to you on the following Monday.

Day 2 of Embryo Development

Normally, we do not provide Day 2 updates but some may receive one because their retrieval was on a Saturday with the update sent Monday. For those who do receive it, below is an explanation for what the three numbers mean. On day 2, your embryos will have developed into more than one cell and the numbers describe the embryo’s appearance.

Example: 411
1st digit = number of cells of the embryo
2nd digit = degree of fragmentation of the cells
3rd digit = symmetry of the cells

Day 3-4 of Embryo Development

During this particularly sensitive period, our embryologists will not be checking for development progress in order to prevent any disturbances in their growth. Sometimes, nature needs time to run its course.

Day 5 of Embryo Development

Typically, 40-50% of embryos will have developed into blastocysts, a key stage due to their much higher pregnancy rates if transferred. But don’t be discouraged if your embryos aren’t there yet! Embryos grow at different rates and some don’t reach blastocyst until a few days later.

If your embryo is behind, our embryologist will continue to culture so long as there is development. If it reaches an arrested state (stops growing), then unfortunately we must discard this embryo as it would not be usable for transfer.

Day 5 Embryo Grading System

  • The first number indicates the stage of development for the embryo / blastocyst:
    6 = Fully Hatched
    5 = Hatching
    4 = Fully Expanded
    3 = Expanded
    1-2 = Early Blastocyst

Day 5 embryos are given one number and two letters, i.e., 4AA.

  • The cells making up the blastocyst are represented by letters: A=Good, B=Fair, C=Poor
    • 2nd Letter = Grade of the embryo (inner cell mass)
    • 3rd Letter = Grade of the placenta component

Though there are occasional exceptions, most culture plans designed by the medical and laboratory team will have your embryos will be frozen once they reach blastocysts stage.