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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 microtools. With the advent of assisted fertilization through micromanipulation, fertilization itself is no longer a hit-and-miss affair. Additionally, embryos can be micro-manipulated for cell biopsy to determine their genetic status as well as aid in their ability to implant through drilling into their outer shell (assisted hatching).

IVF with Intracytoplasmic Sperm Injection (ICSI)

Micromanipulation first saw clinical use in IVF for purposes of assisted fertilization in the treatment of male factor infertility, where fertilization potential was low in cases of poor sperm quality. The ultimate evolution of this approach has been the development of the single sperm injection procedure referred to as Intracytoplasmic Sperm Injection, or ICSI. Using the ICSI technique, the embryologist uses micromanipulation to pick up a single sperm and inject it directly into the egg. This technique is used to fertilize mature eggs in the event of sperm or egg abnormalities.

ICSI allows couples with very low sperm counts or poor quality sperm to achieve fertilization and pregnancy rates equal to traditional IVF. It is also recommended for couples who have not achieved fertilization in prior IVF attempts. Sperm of virtually any quality and from any level of the male reproductive tract may be used with the only criterion for use being that the sperm is alive even if it is not moving (motile). Dead sperm may be able to achieve fertilization; however, the DNA or genetic material from such sperm is too degenerate to form a viable embryo.

Immature sperm from the testicle or the epididymis can be retrieved for use with ICSI for men who possess no sperm in their ejaculated semen (azoospermia). This azoospermia is either due to an obstruction in the tract (obstructive), or to extremely low production of sperm in the testicle itself (non-obstructive). In certain cases, men may produce sufficient sperm, but they do not survive to the point of ejaculation (necrozoospermia). Consequently, instead of using non-viable sperm from the ejaculate, testicular biopsy will provide a ready source of freshly produced viable sperm.

  

ICSI for Non-Male Factor Infertility

The use of ICSI is now routinely applied to a range of clinical situations wherever there is a possibility that conventional in vitro fertilization may be suppressed or not occur. Such situations include the following: idiopathic or unexplained fertility; hyper-responsive ovarian stimulation cases where egg quality may be reduced; post-thaw sperm samples that survive poorly; post-thaw egg insemination; generation of embryos for pre-implantation genetic screening where embryos "clean" from any extraneous contaminating sperm is needed; or, indeed, any case where there is an extreme need to maximize normal fertilization, for example, when a woman has only a few eggs retrieved. It is possible to "rescue" cases following complete failed conventional fertilization with ICSI. The viability potential of these "late-fertilized" embryos is approximately half of timely fertilized embryos; nevertheless, they do generate successful live births. ICSI has become such a common feature of IVF therapy that it is fast becoming the insemination technique of choice.

 

Embryo biopsy

Embryo Biopsy

Briefly, it is of relevance in any discussion of micromanipulation techniques to mention the potential to biopsy both eggs and embryos. This approach is known as preimplantation genetic diagnosis (PGD) and enables the screening of both the unfertilized egg by removal of the first polar body, or the fertilized multi-cellular embryo by removal of one or more cells either at the 6-12 cell stage or from the trophectoderm of the blastocyst. This material can be probed for both genetic mutations or gross chromosomal errors. This technology remains in its infancy and can be of profound importance clinically, but at this time only for cases with very clear medically-defined needs. The biopsy procedure requires very exacting skills of the IVF laboratory, and the egg or embryo is not entirely free of risk during the procedure. Hence, couples whose offspring have a high chance of inheriting a genetic disorder may have their embryos screened. Women who are at risk of generating eggs with a high risk of chromosomal anomalies can benefit from having their eggs or embryos screened for chromosomal normality. While embryos can have their sex determined through this procedure, the GRS team considers it inappropriate to do so except in cases of sex chromosome-linked disorders.

 

Micromanipulation and Assisted Hatching

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.

Assisted hatchingSuch 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. With the advent of more routine transfer of blastocyst stage embryos, the future of this technique, usually carried out on day three of development, may seem in question. Indeed, at the blastocyst stage in vitro, it may be most appropriate to dissolve off the entire zona pellucida prior to transferring naked embryos into the uterus. This could be considered the ultimate form of assisted hatching without the need for micromanipulation. Currently, however, assisted hatching can be easily performed using a 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.

 

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