There exist two types of In Vitro Fertilization (IVF) depending on the method used for egg insemination: conventional or tradicional IVF, and IVF with Intracytoplasmic Sperm Injection (ICSI). That is the main difference between them.
Even though the goal of both fertilization methods is the same, i.e. to create a viable embryo, they are carried out differently, as one shall see in the following sections.
The different sections of this article have been assembled into the following table of contents.
FIV vs. ICSI
Both conventional In Vitro Fertilization and Intracytoplasmic Sperm Injection are subtypes of IVF. However, in practice, people tend to use the abbreviation IVF to refer to the former, whilst ICSI is employed to make reference to the latter. Let's see the motives that led to the emergence of each:
- IVF (traditional IVF) was created to solve determined infertility problems, including Fallopian tube blockage, endometriosis, or certain cases were previous IUI cycles have failed.
- The ICSI procedure (Intracytoplasmic Sperm Injection) was born to treat severe male factor infertility cases, including oligozoospermia or asthenozoospermia, where using other techniques like IUI or conventional IVF fails to lead to successful outcomes.
Even though, as one shall see, ICSI was first created for a determined purpose, today it is widely used as the first option by the majority of clinics, not only when there exists male factor infertility, but also to treat other fertility problems. This is the reason why nowadays conventional IVF is often put at the second level.
In this sense, there exists some controversy between experts in the field. While some are in favor of using ICSI on a regular basis, others bet on conventional IVF as the first choice, leaving ICSI only for particular situations where traditional IVF is unable to lead to success.
Today's trend is to use ICSI in almost all cases. In fact, it is the technique of choice in about 80 percent of the cases that are referred to IVF.
Sperm-egg binding and fusion
The most noticeable difference between these two methods of egg fertilization is the way in which the egg-sperm union occurs in the lab. The ultimate goal is to fuse their nuclei together, resulting in a viable embryo.
In this case, the specialist puts the egg cell together with a drop of semen that contains millions of spermatozoa into an IVF petri dish. Fertilization is expected to occur similarly to the natural process, without further human involvement.
For this to be possible, the sperm vitality and motility parameters should be normal. Otherwise, the sperm might not be able to reach and penetrate the egg coat (i.e. zona pellucida), hit its nucleus, and hopefully lead to the egg-sperm binding.
It it were done using sperm of poor quality, fertilization would never occur. In other words, with low quality sperm, we cannot create viable embryos. In fact, even if an embryo were created, it would be non-viable, that is, its quality would be so poor that it would not be able to cause a full-term pregnancy.
On the other hand, conventional IVF is based on a natural selection process, something that does not occur with ICSI. Only the most powerful, healthy sperm cell will be able to meet the egg and fertilize it.
You might like: Sperm’s Journey to the Egg – How Sperm Meets Egg with Pictures.
Intracytoplasmic Sperm Injection
When IVF with ICSI is used, almost no effort by the sperm is required. For this reason, an optimal sperm quality is not required when this technique is used. Actually, there is only one fundamental requirement—it must be alive.
Under the embryologist's criteria, paying special attention to morphology, the best sperm cell is selected. Then, it is injected with a microinjector inside the egg cell, so that the nuclei of both gametes fuse together, resulting in a viable embryo.
ICSI means taking a step further towards achieving pregnancy. However, the fact that the sperm is directly injected into the egg does not translate into success by default, since it is possible that the nuclei do not fuse together.
Further differences between IVF and ICSI
The way in which the egg and the sperm are brought together creates one more difference between conventional IVF and ICSI: the level of similarity with natural fertilization.
IVF is more similar to the natural fertilization process, since artificial assistance is minimal. Conversely, in the case of ICSI, manipulation by the specialist is required in almost every step of the process. This is an advantage in cases of poor sperm quality, but might be counterproductive in other situations.
There is one more difference between them: oocyte denudation. This process is performed on the oocytes before microinjecting the sperm cell in ICSI procedures. Denudation is used to remove the cells of the cumulus that surround the ovum in order to make sperm microinjection procedure easier.
In conventional IVF cycles, denudation is also performed, but after fertilization, that is to say, on day 1 of embryo development, when the specialist evaluated whether fertilization has occurred correctly.
Finally, one should not forget that ICSI allows fertilization even in the most challenging cases, including those where the sperm sample has been collected via testicular biopsy or epididymal sperm aspiration. With conventional IVF, this would never be possible.
Outcomes and success rates
Although it is true that ICSI reaches good reproductive outcomes in cases where IVF would not, the success rates of each technique vary greatly depending on cases like:
- Expertise of the embryologist or specialist
- Cause of infertility in the woman or couple
- Characteristics of the gametes, egg and sperm included
In clinics where both methods are used, these and other aspects are evaluated before deciding which technique will lead to the most successful outcome on a case-by-case basis.
For instance, if the egg has a thickened zona pellucida, it will be very difficult for the sperm cell to penetrate it. In this case, the ICSI method would provide better results to achieve pregnancy. Also, if the sperm has motility issues (asthenospermia), or if the egg and sperm recognition systems fail, conventional IVF is unlikely to work.
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Inversely, if we use poor-quality oocytes, the manipulation required with ICSI might damage them to a large extent, which could prevent fertilization.
Finally, if the quality of both gametes is good, conventional IVF (a much simpler method) might be enough to achieve pregnancy.
Which is better?
Actually, there is not a better option—it just depends on the particularities of each case. IVF has a series of advantages and disadvantages in comparison with ICSI. So, based on an individual approach, conventional IVF or ICSI will be the best option.
For instance, if PGD (Preimplantation Genetic Diagnosis) is required, it is better to perform an ICSI to prevent that the sperms adhered to the egg in conventional IVF alter the results of the genetic analysis.
Get more info on PGD by clicking the following link: What Is PGD or Preimplantation Genetic Diagnosis?
Also, ICSI is the preferred option when the number of oocytes is too limited, as well as when the sperm sample has been collected via testicular biopsy or from cancer patients.
In accordance with embryologist Víctor Montalvo, the common practice in fertility clinics is to go directly for ICSI in cases where the number of oocytes is too low. The main advantage of ICSI in these cases is that it optimizes the procedure, since the sperm selected is of high quality, that is, with good motility and morphology.
On the other hand, when donor eggs and/or sperm are used, since they are gametes of optimal quality, turning to the technically challenging ICSI technique is unnecessary. Good results will be achieved with just conventional IVF.
Combined cycle: IVF + ICSI
An option that is becoming very popular amongst fertility clinics is IVF with ICSI treatment or just IVF+ICSI, which is a combination of both conventional IVF and ICSI. IVF-ICSI means that both types of fertilization are combined in the same cycle. Thanks to it, we can make the most out of both techniques.
To do this, the set of eggs available is divided into two groups: half of them will be fertilized using conventional IVF, and the other half using ICSI.
It should be noted that IVF+ICSI is an option that is only available when there is a high amount of eggs, and choosing one option over the other is a complicated decision to make.
Also, when the intended mother or parents prefer a process that is more similar to natural fertilization but the characteristics of their situation do not allow it, a cycle if IVF+ICSI is often the solution.
FAQs from users
What are the advantages and disadvantages of ICSI over IVF?
Both techniques are reproductive technologies, and as such, we cannot say that one is better than the other. Actually, it depends on the diagnosis of each couple. In the case of conventional IVF, we put the oocyte in contact with a determined concentration of sperm, so that the sperm itself fertilizes the egg, which resembles natural fertilization to a large extent. In many cases, sperm quality is altered, in which case using the sperm won't be possible. In such situations, we use ICSI. It consists in microinjecting the sperm, which is subjectively selected by the embryologists, into the oocyte.
As regards the number of IVF attempts before giving up, does it vary if it is conventional IVF or ICSI?
Unless fertilization failure has occurred with IVF, we usually take into account all cycles done with both techniques before deciding to move on to another treatment such as egg donation. Even though each patient is different, the average number of IVF attempts recommended is 3 or 4 at our clinic.
What are the success rates of ICSI? What about IVF?
Fortunately, multiple studies have demonstrated fertilization and pregnancy success rates with ICSI are equivalent to standard insemination by IVF.
What is the price difference between conventional IVF and ICSI?
If we take into account that the average cost of basic IVF is about $12,000, the cost of ICSI is usually an additional $1,500 and $2,000.
In the UK, the average cost of ICSI on top of IVF is £500 - £1000. The cost of a single IVF cycle can be £5,000 or more.
Is there any difference in the stimulation step if you use IVF or ICSI?
No, the treatment followed is the same at this point. Broadly speaking, the main steps of both conventional IVF and ICSI are:
- Ovarian stimulation
- Egg retrieval
- Semen preparation
- Egg fertilization, whether conventionally or using ICSI
- Fertilization follow-up
- Embryo culture
- Endometrial preparation
- Embryo transfer
- Cryopreservation of unused embryos
Suggested for you
As we have explained above, the process to follow is almost the same in both conventional IVF and ICSI, except for the oocyte denudation and fertilization steps. Want to learn more about the entire process step by step? Read: The IVF Process – How Is It Done Step by Step?
Likewise, even though we have said that most clinics use ICSI on a regular basis, actually there exist a series of indications for this technique. Find them out here: When Is ICSI Recommended?
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FAQs from users: 'What are the advantages and disadvantages of ICSI over IVF?', 'As regards the number of IVF attempts before giving up, does it vary if it is conventional IVF or ICSI?', 'What are the success rates of ICSI? What about IVF?', 'What is the price difference between conventional IVF and ICSI?' and 'Is there any difference in the stimulation step if you use IVF or ICSI?'.