Fertilization and Continued Embryo Growth
At the time of retrieval, the follicles are aspirated and this fluid is passed to the embryologist in the lab. The eggs are then identified and removed by the embryologist using a microscope and placed into the incubator to avoid exposure to light, and maintain a constant temperature, humidity, and pH level. During this entire process, notes are made on the condition of the eggs. In most cases, two-thirds to three-fourths of the eggs which are retrieved will be mature and ready to be inseminated or injected by ICSI. Immature or post-mature eggs have a much lower fertilization rate. Once retrieved, the eggs remain in the incubator between four and eight hours in order to complete their very final stage of maturation. On the morning of retrieval, a sperm sample is provided by the male partner or via donor sperm, and processed by density gradient washing techniques. This allows for the most viable sperm to be used for insemination or ICSI. One day after retrieval (Day 1), the embryologist begins their day with the assessment of fertilization and by separating out the normally fertilized eggs. Cell division or cleavage will occur after the intermingling of the chromosomes overnight. By Day 2, normally dividing embryos should have four cells. Embryos will be further assessed on Days 2 and 3 for transfer or placement into more advanced blastocyst growth media until day 5 or 6.
Grading of the Embryo
Several factors are used by the embryologist to grade embryos through their development. In general, higher quality embryos have a uniformly smooth appearance under the microscope with smooth membranes. In addition, each of the cells should be approximately the same size. The outside wall of the embryo (zona pellucida) should be clear and not too thick. In some cases, increased amounts of cellular debris called fragmentation can be seen in the outside wall; generally, less fragmentation is better. By Day 3, the embryos are given a grade according to how they look to the embryologist – at Advanced Fertility Care this is a numerical grading system of 1 to 4 with 1 being the best. This assessment gives us a subjective estimate of the likelihood of implantation once the embryos are replaced into the uterus. Those that have the best characteristics and are cleaving normally are believed to have a higher chance of implantation; these will be chosen for transfer.
It must be emphasized that the overall assessment is based on the experience and technical ability of the embryologist and is subjective. Embryos that may appear visually flawed, still have the ability to implant, but at rates less than those with better characteristics. The number of embryos transferred depends on the quality of the embryos, the age of the woman, and the day of transfer (Day 3 vs. Day 5). See section on How Many Embryos to Transfer.
Security in the Laboratory
At Advanced Fertility Care, we are committed to providing a well controlled and secure laboratory environment for your eggs, sperm, and embryos. We utilize multiple monitoring and security systems as well as state-of-the-art filtration systems to maintain our secure “clean-room” environment. Access to our laboratory is limited via card access systems to only key laboratory personnel and the physicians. We make every effort to assure couples that the eggs, sperm, and embryos in our possession in the laboratory are always handled with trust, respect, expertise, and care. Our labeling process and a series of checks and balances are designed to ensure matching you to your eggs, sperm, and embryos. This is a constant priority throughout the IVF process.