Micromanipulation

Advances in microscopic equipment and knowledge about oocytes, sperm and embryos have lead to the development of new techniques in ART. Micromanipulation refers to the microscopic treatment of individual oocytes, sperm, or embryos in an effort to improve fertilization and/or pregnancy rates. These techniques require specialized equipment and personnel. Currently the most common micromanipulation techniques used are intracytoplasmic sperm injection (ICSI), which is used to assist fertilization in cases of severe male factor infertility, and assisted hatching which is used in an effort to facilitate implantation of the embryos.

Intracytoplasmic Sperm Injection

The ICSI technique has been developed over the past 10 years to treat cases of severe male factor infertility. Candidates for ICSI may include patients with severe reductions in sperm number or motility, regardless of cause, and patients with a history of failure of fertilization in conventional in vitro fertilization-embryo transfer (IVF-ET). The ICSI technique may also be used to achieve fertilization using surgically extracted sperm from patients with anatomic or surgical conditions (such as vasectomy) that prevent sperm from entering the ejaculate. In all these cases, donor sperm or ICSI may provide the only options for conception.

The ICSI technique attempts to achieve fertilization by the direct injection of a single sperm into the cytoplasm (interior) of the egg. This is accomplished in the following manner. Mature eggs are freed of surrounding cells by a combination of enzyme treatment and microdissection. Using special micromanipulation equipment, the eggs are individually injected with a single sperm. Injected eggs are returned to the laboratory incubator and are treated thereafter as in conventional IVF-ET.

The mechanical placement of a sperm into the egg bypasses all the normal processes of sperm-egg interaction that occur. These processes normally lead to the selection of the single fertilizing sperm based on its ability to pass through the many layers of cells surrounding the egg, to contact and bind to the egg coating (zona), to penetrate this coating, to contact and merge with the egg cell membrane and ultimately to be drawn into the egg where the genetic material in the sperm joins that of the egg. These interactions help assure that a viable sperm is selected by the egg for fertilization. Even when conventional IVF-ET is performed, the egg is exposed to tens of thousands of sperm. In sperm injection, it is the laboratory that chooses the best appearing sperm. We rely on the size, shape, and motility of sperm to choose the ones for injection. While these characteristics are useful, they do not guarantee that the sperm selected for injection is normal.

The potential consequences of injecting a normal appearing sperm, which is in fact abnormal, include the development of a genetically abnormal embryo. Previous experience suggests that most abnormal conceptions do not implant or develop in the uterus. The incidence of congenital abnormalities (birth defects) following ICSI appears to be no higher than that of the general ART population. This observation is based on the experience of several thousand babies born worldwide following ICSI. However, this issue is an area of ongoing investigation, and it must be recognized that long term risks of the procedure (for example, regarding the child’s fertility) are unknown. Recent evidence suggests that some forms of severe male factor infertility are genetic and may be passed on to male offspring through the ICSI procedure. In addition, you must realize that within the normal human population a certain percentage (approximately 4%) of children are born with physical or mental defects (congenital abnormalities), and that the occurrence of such defects is beyond the control of physicians.

Apart from the possible consequences of selecting an abnormal sperm for injection, the physical trauma to the egg resulting from sperm injection can lead to degeneration of the egg or arrested embryo development. Thus the risk of ICSI should be weighed against the possible benefits.

The benefit of ICSI is that it provides a way to treat extreme cases of male factor infertility which otherwise would remain untreatable. Experience shows that fertilization in vitro requires a minimum number of motile, normal shaped sperm. The chance for fertilization in vitro becomes very low when this minimum number of sperm is not available. Theoretically, only a few sperm are necessary to undertake ICSI. The alternatives to ICSI for treatment of severe male factor infertility are limited. Sometimes all the eggs can be placed in one culture dish with all the available sperm. This is known as “clutch insemination”, which differs from conventional IVF-ET in which each egg is inseminated with a separate batch of sperm. A minimum number of actively moving, normal shaped sperm is still required for fertilization to occur with clutch insemination. Another option is donor sperm. Use of donor sperm normalizes the success of conventional IVF-ET in couples with severe male factor infertility. In cases where male factor is the only diagnosis, pregnancies with donor sperm can be achieved through timed insemination, a treatment far less expensive and complicated than IVF-ET.

There is no guarantee that these inseminations will result in fertilization or a pregnancy. Coexisting female fertility problems can decrease the likelihood of conception. In general, the results of intracytoplasmic sperm injection decline with increasing age of the female partner. This probably reflects the progressive decline in oocyte quality with age of the patient and the older egg's decreased ability to survive the invasiveness of sperm injection. A separate consent form and additional charge are required for ICSI.

Assisted Hatching

Normally, embryos are transferred to the uterus three days after retrieval. Usually the embryos consist of six to eight cells at this stage. After transfer, the embryo must continue to develop to the blastocyst stage (a hollow ball of about 100 cells) before implantation can occur. This development takes several days. Immediately before implantation, the blastocyst must "'hatch" from the zona coating which originally enveloped the oocyte. To assist the hatching process, we micromanipulate the embryos immediately before embryo transfer. This involves dissolving part of the zona coating with an acid solution or cutting it with a fine needle or laser. Trained personnel using specialized micromanipulation tools must perform this under the microscope. There is a small risk of damage to the embryos from the procedure. It is not clear which patients are the best candidates for assisted hatching, and we therefore use the assisted hatching procedure on all embryos to be transferred.

PGD (Preimplantation Genetic Diagnosis)

Preimplantation Genetic Diagnosis (PGD) is a technique that can be used during in vitro fertilization (IVF) procedures to test embryos for genetic disorders prior to their transfer to the uterus. PGD makes it possible for couples or individuals with serious inherited disorders to decrease the risk of having a child who is affected by the same problem. At present, PGD is only offered in a few centers, usually under the supervision of an institutional ethics review board, but its use may become more widespread in the near future.

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