Embryo Development: What Happens After My Egg Retrieval?
Day 0 – FIRM physicians refer to retrieval day as day O of embryo development. Before leaving the recovery area, your FIRM doctor will give you the final egg count. Several hours later an embryologist in the IVF lab will inseminate the eggs. Insemination can be accomplished by standard insemination or by ICSI (shown below). Standard insemination involves placing washed sperm with an egg into the culture dish. ICSI, a more involved process, requires that the embryologist insert the sperm into the egg using a specialized needle and a microscope. After insemination, the eggs are placed back into the incubator to allow time for fertilization to occur. Your FIRM doctor will review with you the method to be used for insemination prior to your IVF cycle. However, on occasion, the results of the semen analysis on the day of the retrieval may necessitate ICSI be done, which your FIRM physician would discuss with you in that event.
Day 2 – Day 2 is what FIRM refers to as fertilization check day. Approximately 16-20 hours a er the insemination process takes place the embryologist will check to see if fertilization has occurred. The embryologist is looking for evidence of 2 nuclei (pn) – one from the egg and one from the sperm (image below; yellow arrows pointing to the two nuclei). This is how we determine if normal fertilization has occurred. Any more or any less nuclei indicates abnormally fertilization and the embryo is not kept in culture. Our embryologists look at the embryos again on day 2, to confirm continued embryo progression which aids your FIRM physician in determining the timing of your embryo transfer (day 3 versus day 5). After day 2, the embryos are placed back into the incubator and are not disturbed until the day of your embryo transfer (or day 5 if you are proceeding with PGS).
Embryos are grown in a specially designed culture medium which contains the proteins and other essential nutrients for embryo development. Successful embryo development requires maintaining an optimal temperature and pH level which is provided by the incubators. Since the embryos are grown in a very small droplet of culture medium it does not take long for temperature or pH level to change which is the reason why FIRM does not look at the embryos on a daily basis.
Day 2 through Day 4 – Between days 2-3 the embryos should be dividing through the multicellular (cleavage) stages of development. On day 4 the embryos should start entering the morula stage when cells start to rapidly divide making it difficult to distinguish the total number of cells. Shortly thereafter, the embryo begins to form a fluid filled cavity (yellow arrow, image below), at which point we call it a cavitating morula. Seeimagesbelow.
Day 5 through Day 7 – Between day 5 and day 7 the embryo should continue to rapidly divide and expand into the blastocyst stage (image below). The cells begin to differentiate into cells that will become the inner cell mass (potential baby) and cells that will become the trophectoderm (future placenta). Day 5 is embryo transfer day. The physician will review the embryology data with you at the time of transfer and will make their recommendations as to which embryo to transfer. If there are embryos remaining in culture following the embryo transfer and you have consented for embryo cryopreservation, the embryologist will cryopreserve any embryos that reach the appropriate blastocyst stage by day 7. After day 7 has passed, you will receive an update from an IVF team member with whether or not embryos were able to be cryopreserved.
Teresa M. Erb, M.D.