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Optimfert, ICSI fertilization
Click to watch a Video explaining why the time of ICSI fertilization matters.

Why the Time of Fertilization matters when performing ICSI.

For decades, most bright brains around the world have been looking for a universal sign for recognizing a “healthy” embryo or eggs (oocytes). In embryology, we know that the time of fertilization matters a lot when performing ICSI.

It is a very complicated effort and it turns out that it is also in vain and useless. Why? Simply because embryonic development is the result of millions of years of evolution and has a tremendous ability to adapt plastically to changing conditions. This means that it can also deal with a number of negative impacts on its development and in each of its development periods it can react to these changes a little differently. The same thing e.g. the change in temperature manifests itself differently in the period before the first division and differently again in the formation of the blastocyst. This could be talked about indefinitely and it is certain that we will not find a single unambiguous feature that would define a healthy embryo for all periods (attention: vice versa – deselection – the selection of an abnormal embryo has such unambiguous features).

Nevertheless, I am convinced that something in the biology of development has a universal character.


Timing. A universal biological phenomenon and its consequences

Translated to humans, this means that all our biological abilities are gradually acquired, reached optimum, and then lost. The ability to conceive is a case in point. Our whole life from cognitive abilities to physical fitness is built on this principle.

Maturation of Oocytes during IVF
ICSI fertilization according to oocyte maturity

At the same time, however, it is also true that these abilities are a cascade of events that must be acquired not only at the right time but also in the right order. There can be no pregnancy without puberty, etc.

It follows that the occurrence of events at the wrong time will have a negative impact on the result, e.g. pregnancy 10 years resp. A 50-year-old will always be riskier than a 25-year-old woman.

This principle also applies to Eggs.  The moment in which they are most receptive of the Sperm cell in order to achieve successful fertilization and ensure a healthy embryo development.


Before ovulation, the egg gradually acquires the ability to be fertilized, which is lost over time. In in-vivo conditions i.e. in natural conception, this happens spontaneously and the sperm “wait” for this optimal time. If they reach their destination late, they will catch the egg outside the optimal time and fertilization will not take place … therefore timed sexual intercourse is often recommended.

Under in-vitro fertilization (IVF) conditions, this optimal time must be determined based on the morphological properties of the egg. The problem, however, is that classical light microscopy is able to distinguish only the presence of the first polar body as a sign of maturity (suitability for fertilization) of the egg. But that is not enough. We know that an egg with a first polar body still does not have to be mature and the exact determination of maturity is only possible using the so-called polarized microscopy (PLM), with which we can non-invasively image the spindle. The spindle is an intracellular structure that is responsible for dividing chromosomes during cell division. In the case of egg development, the spindle is so far the only structure that can be used non-invasively (intravitally) for determination of the optimal time of fertilization.  This is why the time of fertilization matters when performing ICSI.

It is clear from our research that the farther we are from this optimum (backward, but mainly forward, ie prematurely), the more anomalies appear in the embryos created in this way.

Low responder to IVF stimulation- Optimfert
Why the time of ICSI fertilization matters

This phenomenon is most evident in women of older reproductive age (38 and older) with a lower ovarian reserve and lower egg production. In these patients, the results are a smaller number of eggs with a higher proportion of immature forms. In these cases, it is then necessary to wait for the eggs to mature.

In order to be able to determine this optimal time really objectively (as I mentioned light microscopy is not enough), we introduced the OptimFert (optimization of fertilization) methodology at our workplace, which uses PLM to determine the exact properties of the spindle and determine the optimal time of fertilization.

In this way, it is possible to increase the percentage of fertilized eggs and reduce the percentage of abnormal embryos that could be induced due to suboptimal fertilization time.

In the end.

It may seem like a lot in a small area, but my effort is to introduce you to the issue at least a little and we will talk about the rest in any of your questions, which I look forward to.

This is the goal of this counseling center – through knowledge, trust is built.

Confidence, Transparency, and Patience are the key to a successful IVF treatment.

Author of the post
PFC Team

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