Intracytoplasmic sperm injection (ICSI)
Intracytoplasmic sperm injection (ICSI) is the process of injecting a single sperm into an egg. This revolutionary technology enables fertilization in cases where the male partner has low sperm production or motility that cannot be addressed surgically (‘severe male factor infertility’); and in cases where basic in vitro fertilization (IVF) treatment has been unsuccessful. ICSI is always necessary in cases where sperm is surgically removed from the testicles (MESA and TESA procedures).
Since it was first used in the early 1990’s, there have tens of thousands of children born after having been conceived with the use of ICSI. In 2007, 63.5% of all IVF cycles in the United States involved the fertilization of eggs by ICSI.
ICSI and IVF
ICSI is used together with IVF treatment. The female partner is given fertility stimulating medications to produce a number of mature eggs, which are harvested in a minor surgical procedure and held in incubators in our laboratory.
The male partner provides a sperm sample (this usually occurs on the same day as the egg retrieval procedure; however samples can be collected in advance and stored frozen until needed). An embryologist analyzes the sample and isolates the strongest and best swimming (motile) sperm to be used for insemination. In standard (non-ICSI) IVF, about 50,000 sperm are added to each egg in a petri dish, allowing the sperm to penetrate the eggs “naturally.” In cases where the sperm are unable to fertilize the egg on their own, the embryologist can employ ICSI to inject the sperm directly into the egg. If a sperm sample is considered ‘borderline,’ some eggs may be injected while others are given the chance to fertilize naturally in the petri dish.
Fertilizing eggs through ICSI:
- The embryologist removes follicle cells surrounding each egg using an enzyme solution. This is necessary to make sure the egg is mature enough to be injected and for the embryologist to see what they are doing, and so that the egg can be gently grasped for the injection procedure.
- Each egg is held by gentle suction in a glass pipette (figure 1).
- A single sperm is injected through the shell of the egg via a tiny, glass microneedle (figure 2).
- The sperm is deposited deep into the innermost part of the egg (cytoplasm) and the needle is withdrawn (figure 3).
How do I know whether I need ICSI?
The thick, hard shell around the egg (the “zona pellucida”) is difficult for sperm to penetrate even under the best of circumstances. Sperm must be strong swimmers and properly shaped in order to fulfill this task. As part of a basic fertility evaluation, the male partner will have a sperm analysis to assess parameters such as count, motility (movement) and morphology (shape). According to these results, ICSI may be advised. For those who have had their sperm recovered surgically through MESA, TESA or other procedures, ICSI is always necessary.
ICSI is also required when fertilizing previously frozen (or vitrified) eggs. Eggs that have been frozen/vitrified and subsequently thawed will have a hardening of the zona, as a result of exposure to cryoprotectants (like “anti-freeze”) and sub-zero temperatures. In these cases, if ICSI is not performed, the fertilization rates of these eggs will be very low or none at all. ICSI allows previously frozen eggs to be fertilized at normal rates (about 70%).
ICSI is also usually necessary in cases of Pre-Implantation Genetic Diagnosis. When an embryo has to have cells removed to be analyzed for the presence or absence of mutated DNA (for example when the parents are carriers for the genetic diseases Cystic Fibrosis), it is important that there be no contamination of the embryo biopsy specimen with extraneous sperm. Therefore, exposing the egg (and therefore the subsequent embryo) to only one sperm will keep other sperm DNA out of the picture.
ICSI benefits and risks
ICSI enables many couples to achieve fertility and a healthy pregnancy where it otherwise might have been impossible. Fertilization rates, embryo quality and pregnancy rates in those who have had ICSI are identical to those in couples who have had IVF without ICSI.
A small percentage of eggs (<5%) may be damaged or destroyed by the ICSI process. Because ICSI has only been in use since the early 1990’s, long term effects of this procedure are still being studied. Studies published in scientific journals have shown that children born as the result of ICSI are slightly more likely than other children to have sometimes serious genetic abnormalities (6 per a thousand births as opposed to 2 per a thousand births). At this point, it is unknown as to whether this increased risk of chromosome abnormalities is due to the ICSI procedure itself or due to the fact that the male has a severe male factor problem in the first place. Most reproductive biologists believe that it will turn out to be the latter. As ICSI has become more widely employed for IVF fertilization and it’s use has been expanded to less severe cases of male factor infertility, these rates of abnormalities in the offspring have decreased.
Currently, Pacific Fertility Center, located in Northern California's San Francisco Bay Area, employs ICSI in 40% of our IVF cycles. This is two-thirds of the national average. We strongly believe ICSI should only be used for definitive male factor infertility and not for all cases or for low egg numbers. Our rates of fertilization with ICSI are right at 75% which is the same as the national average.