Fertilization of Eggs in the Laboratory
Fertilization of Eggs in the Laboratory
In vitro fertilization literally means “fertilization in glass”. Fluid aspirated from ovarian follicles is examined in the embryology laboratory. The eggs are identified, separated from the hormone producing cells and placed in a specialized nutrient solution. Several hours later, approximately 50,000 -100,000 processed sperm are placed around each of the eggs. The eggs and sperm are allowed to incubate together in a carefully controlled environment. Approximately 16-24 hours later, the eggs are inspected microscopically for fertilization as evidenced by the presence of two nuclear bodies. These binuclear unicellular bodies are referred to as pro-nuclear embryos (also called 2PN).
As stated earlier, ICSI has revolutionized the treatment of male infertility. The procedure involves the direct injection of a single sperm into each egg under direct microscopic vision. The successful performance of ICSI requires a high level of technical expertise. In centers of excellence, when ICSI is employed, the IVF birth rate is unaffected by the presence and severity of male infertility. In fact, even when the absence of sperm in the ejaculate requires that ICSI be performed on sperm obtained through Testicular Sperm Extraction (TESE), the birth rate is no different than when IVF is performed for indications other than male infertility.
The introduction of ICSI has made it possible to fertilize eggs with sperm derived from men with the most severe cases of male infertility and achieve pregnancy rates as high, if not higher than that which can be achieved through conventional IVF. The indications for ICSI have broadened dramatically, with the process now being used for a variety on indications other than male factor infertility. For example, I use ICSI to assist in the fertilization of eggs that are believed to have a hardened or thickened outer layer, called the zona pellucida. This is frequently found in the association with polycystic ovarian syndrome (PCOS) and in eggs derived from older women (over 40 years). ICSI is also frequently recommended in cases of “unexplained infertility” and where there is a history of poor fertilization during one or more prior IVF attempts. Many centers now perform ICSI on all eggs in order to more accurately time development of the embryos from the moment of fertilization.
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