In vitro fertilization (IVF) is an assisted reproduction technique in which, as its name suggests, the fertilization of the ovum occurs in vitro, that is, in the laboratory. This procedure can be carried out in the classical way or by intracytoplasmic sperm injection, known as ICSI or IVF-ICSI for its acronym in English.
The objective of these two IVF methods is the same: to favor the fertilization of the egg by sperm to give rise to an embryo. However, there are differences between both techniques.
Provided below is an index with the 9 points we are going to expand on in this article.
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 where 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.
Currently, ICSI is used widely in numerous clinics. This means that ICSI is not only used for fertility problems in men, but also for other reproductive problems, which has left IVF in the second plane.
In this sense, there is controversy among professionals. There are those who defend the application of ICSI in most cases of infertility and those who are committed to performing IVF whenever possible, leaving ICSI only for situations in which IVF does not offer a solution.
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.
On the other hand, in conventional IVF there is a natural selection of the sperm that fertilizes the egg. This does not happen in ICSI, since in this last technique, as we will see below, it is the embryologist who chooses the sperm to be microinjected.
Intracytoplasmic Sperm Injection
When the ICSI technique is performed, the embryologist selects the one that seems to be the best sperm, especially in relation to its mobility and morphology, to introduce it with the help of a microinjector inside the egg.
In this way, with ICSI, one more step is taken towards fertilization. However, it should be noted that the fact of introducing the sperm directly into the egg does not necessarily imply that fertilization will occur.
In the case of ICSI, high sperm quality is not required, since the sperm will have great help to fertilize the egg.
Other differences between IVF and ICSI
The difference in the way of fusing the egg and the sperm causes the IVF and ICSI techniques to vary in another sense: the similarity with natural fertilization.
IVF is much closer to the physiological process that occurs in a natural pregnancy, since the intervention by the embryologist is less. In the case of ICSI, the manipulation is much greater. This may be an advantage of ICSI in cases of poor semen quality, but it could be counterproductive in other situations.
Finally, we must not forget that ICSI allows fertilization in special cases such as those in which the sperm sample has been obtained by testicular biopsy or epididymal aspiration.
Decumulation of the ovules
There is another difference between IVF and ICSI: the so-called denudation or oocyte decumulation. This is a process that is carried out on the ovules before microinjecting the sperm when the ICSI technique is to be used. Denudation consists of removing the cumulus cells that surround the oocyte, to facilitate the introduction of the sperm into it.
In conventional IVF, decumulation is not performed before fertilization, but after fertilization. The elimination of the cumulus cells in classical IVF is performed on day 1, when it will be evaluated whether or not fertilization has occurred.
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.
If you need to undergo IVF to become a mother, we recommend that you generate your Fertility Report now. In 3 simple steps, it will show you a list of clinics that fit your preferences and meet our strict quality criteria. Moreover, you will receive a report via email with useful tips to visit a fertility clinic for the first time.
Inversely, if we use poor-quality oocytes, the manipulation required with ICSI might damage them to a large extent, which could prevent fertilization.
Is IVF or ICSI better?
There is no one technique that is better than another, but it will depend on each case. IVF has a series of advantages and disadvantages in relation to ICSI and, depending on the personal evaluation of each patient, it will be better to apply one method or the other.
For example, it will be better to apply ICSI when there are few eggs available and in the case of having a valuable seminal sample (such as those obtained by testicular biopsy or in cases of oncological patients).
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 applied in some assisted reproduction clinics is what is known as a mixed cycle or combined fertilization. This alternative consists of performing both IVF and ICSI in the same cycle, which allows taking advantage of the advantages of both processes.
To do this, in the mixed cycle the cohort of ovules obtained is divided into two groups: half will be fertilized by conventional IVF and the other half through intracytoplasmic sperm injection (ICSI).
This method is usually applied when there is a high number of eggs and the conditions do not allow a clear decision to be made for one or the other technique.
The mixed cycle is also chosen when the woman or couple prefers a more natural process, but the characteristics of their situation do not allow it.
FAQs from users
IVF or ICSI, who chooses the technique to be applied in each case and how?
Although until relatively recently the ICSI technique in in vitro fertilization was considered an "extra" (even generating an added cost), today most assisted reproduction laboratories to consider it as one more part of their therapeutic tools. Thus, the team of doctors and embryologists are the ones who usually decide on its use, depending on different criteria, such as quantity and quality of the oocytes obtained, age of the patient, previous decumulation process (to evaluate the maturity of the oocyte extracted), causes of sterility, etc.
How to choose between conventional IVF or ICSI?
Dr. Inmaculada Díez de Ginemed answers us. As the doctor tells us:
In principle it is by mutual agreement with the patient, but it also depends on the reason for which we have passed to an in vitro. The most common cause of insemination failure or failure to get pregnant is fertilization failure. Therefore, today we recommend ICS much more than conventional IVF.
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
We have mentioned that the process to be followed is practically the same for conventional IVF and ICSI, except for the decumulation and the exact way of joining the egg and the sperm. If you want to know the complete procedure followed in these techniques, I recommend that you consult this article:The IVF Process – How Is It Done Step by Step?
On the other hand, although we have said that ICSI is generally applied in most clinics, there are certain indications for this technique. Do you want to know what they are? Click here: When Is ICSI Recommended?
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FAQs from users: 'IVF or ICSI, who chooses the technique to be applied in each case and how?', 'How to choose between 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?'.
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