It has been proposed that a certain number of otherwise viable embryos do not implant simply because they are unable to break free from the surrounding “jelly coat” (zona pellucida) when they reach the blastocyst stage of development. Around an unfertilized egg there exists a transparent glyco-protein coat that acts to protect the egg and regulate normal fertilization by any penetrating sperm. This jelly-like coat continues to protect the early preimplantation embryo until, as a blastocyst, the embryo fills itself up with fluid like a water-filled balloon, pumping itself larger and larger until it ruptures and “hatches” from the zona pellucida. The embryo is now ready to make contact in its naked form with the endometrium and implant. Inappropriate ovarian environment due to advanced maternal age or other factors that may compromise the follicular environment may in certain cases render the zona pellucida thicker or tougher. Such IVF cases may benefit from the application of a form of micromanipulation referred to as “assisted hatching” In this process, the embryo has a hole made in the surrounding zona pellucida prior to transfer to enable it to “hatch” free from the zona pellucida more easily when it expands as a blastocyst in the uterus. This technique has never been unconditionally proven to be effective in any well-defined group of IVF patients, and as such remains essentially an experimental procedure.
Holes in the zona pellucida may be made mechanically, chemically, or by laser. Currently, however, assisted hatching can be easily performed using an infrared laser to create a hole in the zona pellucida that allows the embryo an easy means of escape when it is time to try and implant into the uterine wall.
MICROMANIPULATION IN IVF THERAPY
Micromanipulation is the technique whereby sperm, eggs and embryos can be handled on an inverted microscope stage, performing minute procedures at the microscopic level via joysticks that hydraulically operate glass micro tools.