Egg Fertilization and Embryo Culture
The male partner provides the laboratory with a semen specimen to be used for fertilization of the eggs, except if donor or frozen sperm is used.
In cases of normal sperm function, the eggs and several thousand sperm are placed together in a dish which contains a culture media. These dishes are kept in an incubator overnight and are examined under the microscope on the morning after the egg retrieval to determine which eggs have fertilized normally.
An alternative method of achieving egg fertilization is called Intracytoplasmic Sperm Injection, or ICSI. An extremely sharp glass needle is used to inject one sperm directly into the center (cytoplasm) of the egg under the guidance of a specially fitted microscope.
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ICSI: Intracytoplasmic sperm injection |
Candidates for ICSI include men with (1) severely compromised sperm parameters, including concentration, motility, morphology, or antisperm antibodies; (2) blockage or absence of the vas deferens, where sperm is surgically collected by epididymal aspiration or testicular biopsy for ICSI; (3) those who had low or failed fertilization on prior IVF attempts; and (4) unknown infertility (causes of couple's infertility remain unknown after completing all diagnostic testing).
The success rate with this technique varies considerably among IVF programs and is highly dependent upon the skill of the embryologist performing the procedure.
One of the most important aspects of a successful IVF cycle is the handling of the eggs and embryos outside of the body. Among our standard protocols is the use of sequential media which is designed to physiologically resemble the environment in the female body. Reproducing the human environment aims to minimize the intracellular stress of the embryo, which is necessary for a positive treatment outcome. Specialized environmental conditions are maintained in the IVF laboratory to eliminate contaminants and volatile substances in the air which may adversely affect embryos.
Traditionally, the majority of embryo transfers are performed after 3 days of culture when the embryos have four to eight cells. A concern with this is that Day 3 embryos normally are found in the fallopian tubes, not in the uterus. The embryo first moves into the uterus at about 78-82 hours after ovulation. The implantation process begins about 3 days later, after blastocyst formation and hatching have occurred.
Many of the embryos on culture day three do not have the biologic potential to develop into high quality blastocysts (Day 5 embryos). Therefore, the trend has been to transfer more embryos on day 3 in an attempt to achieve acceptable pregnancy rates. By choosing the optimal blastocysts for transfer on day 5, we can select the embryos with the highest potential for implanting and making a baby.
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The two pronuclei (small circles in the center of the cell) confirm fertilization of the egg (oocyte) has occurred. |
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A four cell embryo. |
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An eight cell embryo, which is usually seen 72 hours after fertilization. |
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A blastocyst after 5 days of Culture |
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