Embryology Development Timeline
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- Day 0: is the day of egg retrieval. On this day the eggs are retrieved from the follicles and are counted and assessed for maturity/quality. The eggs will be inseminated with or without ICSI (Intracytoplasmic sperm injection) approximately 2-4 hours after the egg retrieval procedure. The eggs are then placed in the incubators overnight.
Day 0: Approximately 200,000 sperm are placed in a dish containing an egg. Similar to natural conception, a single sperm will penetrate the outer layer of the egg and cause fertilization. Fertilization causes the hardening of the egg that prevents more sperm from entering.
- Day 0: Using a microscope and a micropipette an embryology picks up a single motile sperm and places it in the egg. This procedure is routinely used in male factor infertility and unexplained infertility.
Day 1: The eggs are assessed for evidence of fertilization. Normal fertilization is evidenced by the presence of two pronuclei, one from the egg and one from the sperm. If there are too few or too many pronuclei, the embryo is considered abnormally fertilized. All normally fertilized embryos are put into a culture media that mimics the tubal fluid found in fallopian tubes and placed in an incubator.
- Day 2: The embryos are assessed for cell division. Most embryos develop 2-4 cells by day 2. Embryos are graded based on an embryologic grading system that incorporates number of cells, cell regularity and degree of fragmentation. The decision whether to transfer the embryos on day 3 or day 5 is made based on the quality and cell division of the embryos.
- Day 3: Embryos on day 3 usually have 4-8 cells. Depending on the number and quality of the embryos, an embryo transfer can be performed on this day. The embryos that are favorably graded are selected to be transferred. Your physician will help you decide how many embryos to transfer based on your history, age and the quality of embryos. In addition, if you are a candidate for PGD/PGS, the embryos can be biopsied on day 3.
- Day 4: The cells within the embryo continue to grow begin to tightly align themselves against each other to form a compact ball of cells, known as a morula or compacting embryo. At this stage it is approximately 12-15 cells. In a natural conception the embryo enters the uterine cavity as a morula.
- Day 5: On day 5, the embryo develops into an early blastocyst or a blastocyst. A blastocyst is an embryonic structure that has developed into 2 main components; an inner cell mass which gives rise to the fetus and the trophoblast which develops into the placenta. A blastocyst transfer is performed on day 5. Remaining viable embryos are cultured to day 6 and can be cryopreserved at that time. In addition, if you are a candidate for PGD/PGS, the embryos can be biopsied on day 3.
- Day 6: All viable, high quality embryos are able to be cryopreserved on Day 6. Any non-viable embryos are then discarded. Day 6 is the last day that an embryo can remain in the laboratory without being transferred or cryopreserved.
- Assisted hatching is a laser guided procedure performed by an embryologist that softens the outer lining of the embryo to facilitate hatching. This procedure is routinely performed on all cycles using frozen embryos.